American football rules


Gameplay in American football consists of a series of downs, individual plays of short duration, outside of which the ball is dead or not in play. These can be plays from scrimmage – passes, runs, punts, or field goal attempts – or free kicks such as kickoffs and fair catch kicks. Substitutions can be made between downs, which allows for a great deal of specialization as coaches choose the players best suited for each particular situation. During a play, each team should have no more than 11 players on the field, and each of them has specific tasks assigned for that specific play.

Objective of the game

The objective of this game is to score more points than the other team during the allotted time. The team with the ball has 4 plays to advance at least 10 yards, and can score points once they reach the opposite end of the field, which is home to a scoring zone called the end zone, as well as the goalposts. If the offense succeeds in advancing at least 10 yards, they earn a "first down" and the number of tries allotted is reset and then they are again given 4 tries to advance an additional 10 yards, starting from the spot to which they last advanced. If the offense does not advance at least 10 yards during their 4 downs, the team without the ball regains control of the ball.
On offense, points are scored by advancing the ball into the opponent's end zone for a touchdown, or by kicking the ball from the playing field through the raised vertical posts which are most commonly situated on the end line of the end zone for a field goal. After scoring a touchdown, the offense is given an additional opportunity from the 2-yard line to attempt to score. Conversion attempts are used to score 1 or 2 points as follows:
While the opposing team has possession, the defense attempts to prevent the offense from advancing the ball and scoring. If an offensive player loses the ball during play or the ball is caught by a defensive player while still in the air, the defense may attempt to run into the offense's end zone for a touchdown. The defense may also score points by tackling the ball carrier in the offense's own end zone, called a safety.

Time of play

Collegiate and professional football games are 60 minutes long, divided into four quarters of 15 minutes each. In high school football, 12 minute quarters are usually played. The clock is stopped frequently, however, with the result that a typical college or professional game can exceed three hours in duration. The referee controls the game clock and stops the clock after any incomplete pass or any play that ends out of bounds. In addition, each team is allowed 3 timeouts in each half that they may use at their own discretion. The clock normally runs during the action of plays, with a few exceptions known as untimed plays. Some high schools employ a mercy rule in which the clock runs continuously after one team's lead over the other achieves a certain number of points. In these instances, the clock only stops for injuries, or time outs called by a team or a referee.
The clock may also be stopped for an officials' time-out, after which, if the clock was running, it is restarted. For example: if there is a question whether or not a team has moved the ball far enough for a first down, the officials may use a measuring device to determine the distance. While this measurement is taking place, the officials will signal for a stoppage of the clock. Once the measurement is finished and the ball is placed at the proper location, the referee will then signal for the clock to restart. Additional situations where officials may take a time-out are to administer a penalty or for an injured player to be removed from the field.
In addition to the game clock, a separate play clock is also used. This counts down the time the offense has to start the next play before it is assessed a penalty for delay of game. This clock is typically 25 seconds from when the referee marks the ball ready for play. The NFL and NCAA use a 40-second play clock that starts immediately after the previous play ends, though, for certain delays, such as penalty enforcement, the offense has 25 seconds from when the ball is marked ready. The purpose of the play clock is to ensure that the game progresses at a consistent pace, preventing unnecessary delays. Overall, clock management is a significant part of the game; teams leading toward the end of the game will often try to run out the clock while trailing teams attempt the opposite.
Officials also call for media time-outs, which allow time for television and radio advertising. They also stop the clock after a change of possession of the ball from one team to the other. Successful PATs, a field goal try, or a kickoff may also warrant stopping the clock. If an instant replay challenge is called during the game, the referees signal for a media time out. The referee signals these media time-outs by first using the time out signal, then extending both arms in a horizontal position.
Teams change ends of the field at the end of the first quarter and the end of the third quarter, though otherwise, the situation on the field regarding possession, downs remaining and distance-to-goal does not change at these occasions. Separating the first and second halves is halftime. Both halves, and any overtime, begin with kick-offs — the kicking team is decided by a [|coin toss].
In the NFL, an automatic timeout is called by the officials when there are two minutes left in both the second and the fourth quarters, and overtime; this is most commonly referred to as the two-minute warning. No such warning is normally given in amateur football, though if there is no visible stadium clock, the referee will give a two-minute warning.

Overtime

NFL

If a game is tied at the end of four quarters, overtime is played. In overtime, a coin toss is used to determine which team will possess the ball first. The winner of the coin toss can choose to give the ball or receive the ball. If the first possession results in a touchdown or safety, the scoring team wins. If the receiving team fails to score and loses possession, the game goes into sudden death, and first to score wins.
However, if the initial receiving team only scores a field goal, the game is not automatically over and the other team is given an opportunity to possess the ball as well. The other team can win with a touchdown, tie with a field goal leading to sudden death or lose if they fail to score.
During the regular season in the NFL, one overtime period is played. If both teams are tied after the 10-minute overtime, the game officially ends in a tie. Before the season, there was 15-minute overtime. In the playoffs, 15-minute overtime periods continue until a winner is determined. Overtime follows a three-minute intermission after the end of the regulation game. Prior to the start of overtime, a coin flip is performed in which the captain of the visiting team calls the toss. The team that wins the coin flip has the option either to receive the kickoff or choose the side of the field they wish to defend. Ties are rare in the NFL; a game between the Arizona Cardinals and Detroit Lions on September 8, 2019, ended in a 27-all draw. See List of NFL tied games for more games.
Prior to the 2010 playoffs, the overtime winner was simply the first team to score any points; however, the rules were changed to reduce the advantage obtained by the team that won the overtime coin toss. Under the prior rules, the team that won the coin toss would usually elect to receive the ball, then gain just enough yardage to win the game by kicking a field goal without the other team ever touching the ball. The coin toss winner won approximately 60% of overtime games under that rule. In practical effect, the "coin toss" were determining the winner of the game.
The first overtime game played under a trial of the new overtime rules occurred in the between the Denver Broncos and Pittsburgh Steelers at Sports Authority Field at Mile High, Denver, Colorado. Denver won the game on the first play in overtime, an 80-yard touchdown passes from Tim Tebow to Demaryius Thomas. The rule was formally adopted for the 2012 season, and the first game in which both teams scored in overtime was a 43–37 victory by the Houston Texans over the Jacksonville Jaguars on November 18, 2012.
The rules for overtime changed for the 2016–2017 season and were tweaked again for the 2017–2018 season. The NFL's overtime rules are still subject to criticism, as a team that loses the coin toss and goes on to concede the touchdown does not get a chance for their offense to take the field.
Super Bowl LI was the first Super Bowl to go into overtime with a 28-all tie between the Atlanta Falcons and New England Patriots, which the Patriots eventually won with James White scoring a touchdown on the Patriots' first drive.
The 2018-19 NFC and AFC championship games both went to overtime, the first time for such an occurrence. In the NFC title game, the New Orleans Saints won the coin toss but an interception allowed the Los Angeles Rams to drive into range to kick the winning field goal. In the AFC Championship held later that day, the New England Patriots won the coin toss and on their first drive scored the winning touchdown over the Kansas City Chiefs.

NFL Europa

, a defunct league run by the NFL, used a 10-minute overtime period, with the constraint that each team must have the opportunity of possession; once both teams have had such an opportunity, the overtime proceeds in a manner similar to the NFL's. Thus, if Team A has the first possession of overtime and scores a touchdown and converts their kick, Team A would then kick off to Team B. Team B would have to match or exceed the 7 point difference within this ensuing possession; exceeding it would end the game immediately while matching the difference would result in a kickoff to Team A. From this point, the overtime is sudden death. The defunct United Football League had also used this rule.

World Football League

The defunct World Football League, in its first season of 1974, used an overtime system more analogous to the system long used in international soccer. The overtime consisted of one 15-minute period, which was played in its entirety and divided into two halves of 7½ minutes each, with each half starting with a kickoff by one of the teams. The league changed to the NFL's sudden-death format for its final season in 1975.

College and high school

In college and high school football, an overtime procedure to declare that they will take the ball first or second, or 2) to decide on which end of the field the series will occur. The losing team will have the first option in any subsequent even-numbered overtime. In the first overtime, the team with the first series attempts to score either a touchdown or a field goal; their possession ends when either a touchdown or a field goal have been scored, they turn the ball over via a fumble or an interception, or they fail to gain a first down. After a touchdown, a team may attempt either an extra-point or a two-point conversion. However, if the team on defense during the first series recovers a fumble and returns it for a touchdown, or returns an interception for a touchdown, the defensive team wins the game. Otherwise, regardless of the outcome of the first team's series, the other team begins their series. If the score remains tied after both teams have completed a series, the procedure is repeated. If the score remains tied after double overtime, teams scoring touchdowns are required to attempt a two-point conversion for the next two overtime periods. Just as in regulation, if a defensive team recovers a fumble/returns an interception to the end zone during a two-point conversion attempt, they will receive two points. Starting in 2019, if the game is still tied after four overtime periods, each team attempts one 2-point conversion per period rather than getting the ball at the 25-yard line.
In high school football, individual state associations can choose any overtime format they want, or even elect to not play overtime at all. However, most states use the Kansas Plan. In a majority of states, each team is granted possession of the ball at the 10-yard line, meaning that a team cannot make a first down without scoring except via a defensive penalty that carries an automatic first down. As is the case with the college overtime rule, the team that wins the coin toss will have the choice as to whether to take the ball first or second, or decide at which end of the field the overtime will be played. The other major difference between overtime in college football and high school football is that in some states, if the defense forces a turnover, the ball is dead immediately, thus eliminating the possibility of scoring. However, in Texas, the college overtime rule is used, as both the University Interscholastic League, which governs interscholastic activities for Texas public high schools, and the Texas Association of Private and Parochial Schools, the largest analogous body for Texas private high schools, play by NCAA football rules with a few modifications for the high school level.

XFL

The original incarnation of the XFL used a modified Kansas Plan which, upon the first team scoring, required the opponent to score the same or greater number of points in the same or fewer downs. Each team started at the 20-yard line, but like high school, there were no opportunities for first downs. The league also banned field goals except on a fourth down.
The XFL's current incarnation uses a five-round shootout of two-point conversions similar to a penalty shootout in soccer or ice hockey. Such a shootout had never been attempted in organized football at the time the rule was proposed; in April 2019, the NCAA adopted a similar concept for games that reach the fifth overtime starting with the 2019 FBS season. The defense is not able to score, as should a turnover occur, the play would be dead. Defensive penalties result in the ball moving up to the 1-yard line, while a second defensive penalty on any play, even in future rounds, results in a score awarded to the offensive team. To speed up the overtime process, both teams' offense and defense are on the field at the appropriate end zone. Once one team's offense has completed its round of the shootout, the other team's offense plays its round from the opposite end zone. These overtime rules ensure that both teams have an opportunity to win the game and would limit overtime to 5 or 6 minutes. If both teams remain tied after five rounds, multiple rounds of conversions will be played until one team succeeds, thus ensuring that no game can end in a draw.

Playing the game

Coin toss

Three minutes before the start of the game, the referee meets with captains from both teams for a coin toss. The visiting team calls the toss. The winner of the toss may defer their choice to the start of the second half, or they may take the first choice of:
  1. Receiving the kickoff to start the game, or kicking off to start the game
  2. Choosing an end of the field to defend in the first quarter
The loser of the toss gets the remaining option.
At the start of the second half, the team that did not choose first gets the first choice of options.
According to USA Today, in college games, the team that wins the toss defers their choice to the start of the second half over 90% of the time.
If a game goes to overtime, a coin toss is held before the start of overtime, but tosses are not held before the start of subsequent overtime periods. In college, for example, the loser of the toss to start overtime has the first choice in the second overtime period. The choices available to the captains in overtime vary among the NFL, college, and various states' high school rules.
In high school, the coin toss may be held between the captains or coaches earlier before the start of the game. At three minutes before kickoff, the captains meet for a simulated coin toss, where the referee announces the results of the earlier toss.

XFL

The original incarnation of the XFL did not implement a coin toss; instead, an event took place called the "opening scramble", in which one player from each team fought to recover a football 20 yards away to determine possession. Both players lined up side-by-side on one of the 30-yard lines, with the ball being placed at the 50-yard line. At the whistle, the two players would run toward the ball and attempt to gain possession; whichever player gained possession first was allowed to choose possession.
The XFL's current incarnation also does not feature coin tosses. Instead, the home team is given the option to kick off, receive, select a goal, or defer to the second half. In the event of overtime, the visiting team is given the choice of going first or second or selecting which end zone to attack.

Downed player

The rules vary from the college level to the professional level. In the NFL, unless a player is tagged by an opposing player or gives himself up, he is not down. A player carrying the ball is downed when any of the following occurs:
The majority of a football game takes place on plays, or downs, that begin at the line of scrimmage. The officials spot the ball on the line of scrimmage and declare it ready for play.

Positions

The width of the spotted football defines the width of the neutral zone, an area of the field no player other than the snapper may position himself in or above before the snap. Each team has its own line of scrimmage, thought of as a vertical plane from sideline to sideline that passes through the point of the ball nearest its own goal line.
while the defense is in the 4–3 formation. There are many different formations the players may take.
A typical offense is made up of a quarterback, five offensive linemen, two wide receivers, a running back, a fullback, and a tight end, however teams will vary their personnel on the field to fit any given play. A quarterback is essentially the leader of the offense. It is most often their responsibility to pass along the play called to the rest of the players in the huddle before any given play. A quarterback is the primary ball-handler on offense. It is their responsibility to call the snap count for the ball to enter play. Once the ball is hiked into play, it is their job to either hand the ball off to one of their running backs, or scout the field for an open receiver to throw the ball to. In some instances, the quarterback will run the ball themselves. A quarterback is guarded by their offensive linemen. The offensive line is made up of a left and right tackle, a left and right guard, and a center. It is the center's responsibility to hike the ball to the quarterback. An offensive line has two different jobs. When the offense runs a pass play, it is their job to guard the quarterback from the defense that is rushing. When the offense runs a run play, it is their job to clear a path for the running back to run through. The running back also has multiple roles. They will either take the ball from the quarterback and run, move up and help the offensive line block or go out and catch a pass. While the role of the fullback is deteriorating currently among professional leagues, it is their primary responsibility to lead the running back. Running backs and fullbacks are sometimes also called a halfback, a wingback, or a slotback. Like the running back, the tight end also has multiple roles. They will either help the offensive line protect the quarterback, block on run plays, or run or catch the ball themselves. The wide receivers' primary role is to run out into the field of play and catch the ball, although they will also block in some instances.
The players on offense must arrange themselves in a formation, all behind their line of scrimmage. For reasons of safety and competitive balance, there are strict rules which define the way in which the offensive players may line up. Seven players must line up directly on the line of scrimmage while four players line up behind the line of scrimmage. Within this formation, there are six eligible receivers who may receive a forward pass during play. These eligible receivers are either the running back, fullback, tight end, or wide receivers. The remaining five linemen, often called interior linemen do not normally handle the ball during a play. Because of these rules, various leagues of American football have enacted strict rules of uniform numbering so officials may more easily judge which players were eligible and which were not at the start of a play. For example, in college football, ineligible players wear numbers 50–79, while eligible receivers wear 1–49 or 80–99. Even within this structure, offenses can still present a wide number of formations, so long as they maintain the "seven and four" arrangement. Receivers, for example, may play close to the other linemen or they may play some distance down the line of scrimmage, where they would sometimes be called split ends. Of the four backs, they may play behind the linemen or may play "split out" to provide additional wide receivers. These additional receivers can be flankers or slot receivers if they play in the "slot" between the split end and the rest of the offensive line.
The players on defense may arrange themselves in any manner, as long as all players are "behind the line". Players who line up opposite the offensive line are called defensive linemen, usually with one or two defensive tackles in the middle and with one defensive end on each side. A defensive lineman's job is typically to put pressure on the opposing team's quarterback by rushing the offensive line. The defensive line is also most often the first set of players the opponent must get through should they choose to run the ball. Behind the linemen are the linebackers. A linebacker's job can be any number of things, including trying to rush the opposing team's quarterback, stopping the opponents running back on run plays, or covering the opponent's tight end or wide receivers. Positioned opposite the wide receivers are the cornerbacks. Their primary responsibility is to cover the wide receivers. Farthest back from the line are the safeties, usually in the middle of the field behind the linebackers. The safeties are the last line of defense against the opponent. Like a linebacker, a safety's role can vary, however, their most common role is to help the cornerbacks cover the opponent's wide receivers, which is called "double coverage". The linemen and linebackers close to the line of scrimmage, are often referred to as playing "in the box". Players outside "the box" are collectively referred to as the "secondary".

Starting the down

A scrimmage down begins with a snap, where the center throws or hands the ball back to one of the backs, usually the quarterback. The quarterback then either hands the ball off to a back, throws the ball, or runs with it himself. The down ends when the ball becomes dead. The ball is typically next spotted where the ball became dead; however, if it became dead outside the hash marks, it is brought in on the same yard line to the nearest hash mark. This spot becomes the line of scrimmage for the next play. In the case of an incomplete forward pass, the ball is returned to the spot where it was last snapped to begin the next play. A fumbled ball that goes out of bounds is declared dead and possession remains with the team that most recently had control of the ball.

Dead ball

The ball becomes dead, and the down ends, when:
The nearest official typically blows his whistle after the ball becomes dead to alert the players that the down has already ended. If the ball is alive and the official sounds an inadvertent whistle, then the ball still becomes dead, but the team in possession of the ball may elect to have the down replayed or take the spot where the ball was declared dead. If the ball was loose from a fumble, then the ball can be put into play at the spot of the fumble. If the ball was in flight from a kick or a pass, then the down is always replayed.

Free kick downs

A free kick is a down that does not occur from scrimmage. The kicking team begins behind the ball, while the receiving team must remain at least 10 yards downfield before the ball is kicked.

Kickoffs

A kickoff is a type of free kick where the ball is placed on a tee at the kicking team's 35-yard line. In the 2011 NFL Season, changes were made regarding kickoffs to limit injuries. Kickoffs were returned from the 30-yard line to the 35-yard line, repealing a 1994 rule change. In addition, players on the kickoff coverage team cannot line up more than a specified distance behind the kickoff line. This distance is 5 yards at most levels of the game and 1 yard in the NFL, minimizing running starts and thus reducing the speed of collisions. The kicking team's players may not cross this line until the ball is kicked; members of the non-kicking team are similarly restrained behind a line 10 yards further downfield. A valid kickoff must travel at least this 10-yard distance to the receiving team's restraining line, after which any player of either team may catch or pick up the ball and try to advance it before being downed. In most cases, the ball is kicked as far as possible, after which a player of the receiving team is usually able to secure possession. Occasionally, for tactical reasons, the kicking team may instead choose to attempt an onside kick, in which the kicker tries to kick the ball along the ground just over the required 10-yard distance in such a manner that one of his own teammates can recover the ball for the kicking side. If it is touched before ten yards, the ball is dead and a re-kick or spot of the ball will be rewarded to the receiving team.

Receiving a kickoff

A member of the receiving team gaining possession of the ball on a kickoff may attempt to advance it as far as he can toward the kicking team's goal line before being downed. Once the ball carrier is downed, the play is whistled dead and the ball is placed by the officials at the point where the play ended; this spot then becomes the line of scrimmage for the ensuing play. A kick that travels through or goes out of bounds within the end zone without being touched, or is caught by the receiving team in the end zone but not advanced out of it, results in a touchback; the ball is then placed at the receiving team's 25-yard line, which becomes the line of scrimmage. In college football only, a fair catch by the receiving team between its own 25-yard line and the goal line is treated as a touchback, with the ball placed at the 25.
A kickoff that goes out of bounds anywhere other than the end zone before being touched by the receiving team is an illegal kick: the receiving team has the option of having the ball re-kicked from five yards closer to the kicking team's goal line, or they may choose to take possession of the ball at the point where it went out of bounds or 30 yards from the point of the kick, whichever is more advantageous.

Other free kicks

A free-kick is also used to restart the game following a safety. The team that was trapped in its own end zone, therefore conceding two points to the other team, kicks the ball from its own 20-yard line. This can be a place kick, drop-kick, or punt.
In the NFL and high school, a free kick may be taken on the play immediately after a fair catch; see "fair catch kick" below.

Scoring

Scrimmage plays and kickoffs

Most standard football plays are considered sscrimmage plays, initiated from a line of scrimmage. Exceptions are kickoffs and try plays. Although similar rules apply during a try play, the number of points awarded for each score differs on a try play.

Touchdown (6 points)

A touchdown is earned when a player has legal possession of the ball and the ball touches or goes over the imaginary vertical plane above the opposing team's goal line. After a touchdown, the scoring team attempts a try play for 1 or 2 points. A successful touchdown is signaled by an official extending both arms vertically above the head. A touchdown is worth six points, except in the defunct WFL where it was worth seven points.
For statistical purposes, the player who advances the ball into or catches it in the end zone is credited with the touchdown. If a forward pass was thrown on the play, the throwing player is also credited with a passing touchdown.

Field goal (3 points)

A field goal is scored when the ball is place kicked, drop kicked, or free kicked after a fair catch or awarded fair catch between the goalposts behind the opponent's end zone. The most common type of kick used is the place kick. For a place kick, the ball must first be snapped to a placeholder, who holds the ball upright on the ground with his fingertip so that it may be kicked. Three points are scored if the ball crosses between the two upright posts and above the crossbar and remains over. If a field goal is missed, the ball is returned to the original line of scrimmage or to the 20-yard line if that is further from the goal line, and possession is given to the other team. If the ball does not go out of bounds, the other team may catch the kicked ball and attempt to advance it, but this is usually not advantageous. One official is positioned under each goalpost; if either one rules the field goal no good, then the field goal is unsuccessful. A successful field goal is signaled by an official extending both arms vertically above the head. A team that successfully kicks a field goal kicks off to the opposing team on the next play.

Safety (2 points)

The uncommon safety is scored if a player causes the ball to become dead in his own end zone; two points are awarded to the opposing team. This can happen if a player is either downed or goes out of bounds in the end zone while carrying the ball, or if he fumbles the ball, and it goes out of bounds in the end zone. Safety is also awarded to the defensive team if the offensive team commits a foul which is enforced in its own end zone. A safety is not awarded if a player intercepts a pass or receives a kick in his own end zone and is downed there. This situation, in which the opponent caused the ball to enter the end zone, is called a touchback; no points are scored, and the team that gained possession of the ball is awarded possession at its own 25-yard line. If the interception or reception occurs outside the end zone, and the player is carried into the end zone by momentum, the ball is placed at the spot of the catch, and no safety is awarded. A safety is signaled by a referee holding both palms together above the head, fingertips pointing upwards. After a safety, the team that conceded the safety kicks a free kick from its 20-yard line.

Try plays

A try play, more commonly referred to as an extra-point attempt, PAT, conversion attempt, or two-point conversion attempt, based on the scoring team's intentions on the play, is awarded to the scoring team immediately following a touchdown. This un-timed down is an opportunity to score additional points.
The offensive team may attempt to kick the ball through the goalposts, in the same manner, that a field goal is kicked during a scrimmage play. In the NFL, the ball is spotted at the 15-yard line. In college and high school, the ball is spotted at the 3-yard line. If successful, the team is awarded 1 point, referred to as an extra point. This option is almost always chosen because a two-point conversion attempt is much riskier. Since the extra point is almost always successful, sportscasters will often refer to a team-up or trailing by seven points as being "up/trailing by a touchdown".

Two-point conversion (touchdown - 2 points)

The offensive team may attempt to advance the ball via run or pass into the end zone, much like a touchdown on the extra-point attempt, except that it receives two points. This is called a two-point conversion. If the offense elects to attempt a two-point conversion on the try play, the ball is spotted at the 2-yard line in the NFL and on the 3-yard line for college and high school. The success rate for two-point conversions is about 48 percent in the NFL, making the two-point conversion attempt a risky tactic; thus it is usually attempted only when two points will help the team but one point will not.
Under college and NFL rules, if the defensive team gains possession and advances the ball the length of the field into the opposite end zone on the try play, they score two points. This is officially recorded as a defensive conversion scored by the defense. The NCAA adopted this rule in 1988; the NFL added this in 2015.
A safety scored on a try play is worth one point. This can occur when, for example, the defense gains control of the ball and advances it into the field of play, but then retreats into its own end zone when play is stopped. Similarly, the defense could recover a fumble in its own end zone before play is stopped. A safety on a try play could also be awarded to the defense if the defense takes possession of the ball during a try play, advances it all the way down to the opposite end of the field, where the offensive team then regains possession before the play is declared dead in that end zone.

Officials signals on try plays

The officials' signal for a successful try, whether an extra point or a two-point conversion, is the same as for a touchdown. The officials' signal for a safety on a try play is also the same as on a scrimmage play.
After the trial, the team that scored the touchdown kicks off to the opposing team. Unlike a safety that occurs on a scrimmage play, no free-kick is awarded following a safety on a try play.

Try play rules in overtime

During sudden-death over time, particularly in the NFL, if a team scores a touchdown in the overtime period, the game is immediately over, and the try is not attempted.
In NCAA overtime, if the second team to possess the ball in the overtime scores a touchdown which puts them ahead of the opponent in points the game ends immediately and no try is attempted.

Fair catch kick

A free-kick may be taken on the play immediately after any fair catch of a punt. In the NFL, if the receiving team elects to attempt this and time expired during the punt, the half/overtime is extended with an untimed down. The ball must be held on the ground by a member of the kicking team or drop kicked; a tee may not be used.. This is both a field goal attempt and a free-kick; if the ball is kicked between the goalposts, three points are scored for the kicking team. This is the only case where a free kick may score points. This method of scoring is extremely rare, last successfully completed in the NFL by Ray Wersching in 1976. It is only advantageous when a team catches a very short punt with very little time left. A team is unlikely to be punting with only a few seconds left in a half or overtime, and it is rarer still for punts to be caught near field goal range. The officials' signal for a successful fair catch kick is the same as for a field goal.

Defunct leagues

The game is officiated by a crew of three to seven officials. Every crew will consist of a referee, who is generally in charge of the game and watches the action on the quarterback and in the offensive backfield; an umpire, who handles spotting the ball and watches the action on the offensive line; and a head linesman, who supervises the placement of the down box and line-to-gain chains. The crew may also consist of a line judge, back judge, field judge and side judge, in the order listed: i.e. a crew of five officials have a referee, umpire, head linesman, line judge, and back judge.
Officials are selected by the teams in advance or appointed by the governing league. While the majority of officials at lower levels only officiate games on a part-time basis, the NFL is implementing a new system where seven officials will become full-time employees of the league, one for each official position. In the other three major North American professional sports leagues – Major League Baseball, the NBA and NHL – officials are employed by their respective leagues. The sheer volume of games in the other three sports necessitates full-time officials; the NFL regular season is only 16 games long, compared to 162 games for MLB and 82 for the NBA and NHL.
During the game, the officials are assisted in the administration of the game by other persons, including a clock operator to start and stop the game clock ; a chain crew who hold the down indicator and the line-to-gain chains on the sideline; and ball boys, who provide footballs to officials between downs. These individuals may be provided by the teams involved – it is common for a high school coach's son or daughter to act as a ball boy for the team.

Fouls and their penalties

Because football is a high-contact sport requiring a balance between offense and defense, many rules exist that regulate equality, safety, contact, and actions of players on each team. It is very difficult to always avoid violating these rules without giving up too much of an advantage. Thus, an elaborate system of fouls and penalties has been developed to "let the punishment fit the crime" and maintain a balance between following the rules and keeping a good flow of the game. Players are constantly looking for ways to find an advantage that stretches the limitations imposed by the rules. Also, the frequency and severity of fouls can make a large difference in the outcome of a game, so coaches are constantly looking for ways to minimize the number and severity of infractions committed by their players.
It is a common misconception that the term "penalty" is used to refer both to an infraction and the penal consequence of that infraction. A foul is a rule infraction for which a penalty is prescribed. Some of the more common fouls are listed below. In most cases when a foul occurs, the offending team will be assessed a penalty of 5, 10, or 15 yards, depending on the foul. Also, in most cases, if the foul is committed while the ball is in play, the down will be replayed from the new position But if a defensive foul results in the ball advancing beyond the offense's first-down objective, the next play will be the first down of a new series. Some penalties, however, require a loss of down for the offense; and some defensive fouls may result in an automatic first down regardless of the ball position.
In all cases, the non-offending team is given the option of declining the penalty and letting the result of the play stand, if they believe it to be more to their advantage. For some fouls by the defense, the penalty is applied in addition to the yardage gained on the play. Most personal fouls, which involve danger to another player, carry 15-yard penalties; in rare cases, they result in offending players being ejected from the game. In the NFL, if a defensive foul occurs after time has expired at the end of a half, the half will be continued for a single, untimed play from scrimmage. Under college rules, any accepted penalty when the time has expired at the end of any quarter results in an extension for one untimed down.
In the NFL, with three exceptions, no penalty may move the ball more than half the distance toward the penalized team's goal line. These exceptions are defensive pass interference, intentional grounding, and offensive holding – but in this last case, the exception pertains only if the infraction occurs within the offensive team's own end zone, in which case an automatic safety is assessed. Under college rules, the same half-the-distance principle applies, but any offensive fouls involving contact in their end zone result in a safety.

Timeouts

Each team receives three timeouts per half, making for a total of six timeouts per team in a regulation game. Unused timeouts may not carry over to the second half or overtime. In professional football, a team must have at least one remaining timeout to challenge an official's call.

Instant replay

In the NFL, a number of rulings can be reviewed by officials or challenged by coaches. If a coach wants to challenge a play, he must do so before the next play begins, and he does so by throwing a red flag similar to the officials' yellow flags. Coaches are allowed two challenges per game and are granted a third if their first two are successful. The team loses a timeout if they lose the challenge. Therefore, they cannot challenge if they do not have timeouts. Plays within the two-minute-warning and overtime cannot be challenged; any review must be initiated by a replay official off-field. The referee performs the actual review via a video screen on the sideline. The referee will announce the result of instant replay reviews over his wireless microphone.
Beginning in the 2011 NFL Season, an instant replay review by the booth official will now be automatic for every play ruled by the referees on the field to have scored points. This is seen as another step in the "modernization" of sports. Every scoring play will be reviewed now, which saves coaches from using up their challenges on close plays in the endzone. And since the 2012 season, the booth official also reviews all turnovers during the game.
In college, coaches are allowed one challenge per game by first requesting a timeout. Otherwise, a replay official in the press box observes all plays. If he deems a ruling may be in error, he notifies the officials on the field to interrupt the game before the beginning of the next play. The replay official performs the review and relays the decision to the referee, who announces the result. Not every conference employs replay, which is optional.
High school rules generally do not provide for a video review of any decisions by officials during a game. By state adoption, replay may be used in a state championship game. At all times, the use of television or videotape for coaching purposes during the game is prohibited. If a coach feels a rule has been misinterpreted, he may call a timeout and request a coach-referee conference to discuss the ruling with the referee, but no replay equipment will be consulted during the conference.

Major rule differences between NFL and college football

Some of the major rule differences between NFL and college football include:
NFLCollege football
Feet in-bounds required for a completed passTwoOne
Down-by-contact ruleYes, a player is active until he is tackled or forced down by a member of the opposing teamNo, a player is automatically ruled down when any part of his body other than the feet or hands touches the ground
Penalty for defensive pass interferenceAutomatic first down at the spot of the foulAutomatic first down, with the lesser of 15 yards from the previous spot or the spot of the foul
Clock temporarily stops after a first downNoYes
Line of scrimmage following a missed field goalThe greater of the spot of the kick or the opposing team's 20-yard lineThe greater of the previous line of scrimmage or opposing team's 20-yard line
Two-minute warningYesNo
Starting point of a one- or two-point conversion2-yard line on 2-point conversions; 15-yard line on 1-point conversions3-yard line
OvertimeModified sudden death: if the team possessing the ball first scores a field goal, the other team is given one possession to win with a touchdown or continue the game by scoring a field goal.
In the regular season, only one 10-minute overtime is played and games may end in a tie. Postseason games play multiple 15-minute periods until there is a winner.		Each team is given one possession from its opponent's twenty-five-yard line with no game clock. The team leading after both possessions is declared the winner. If the teams remain tied, another overtime is played. Starting with triple overtime, teams are only allowed to attempt two-point conversions after a touchdown. After quadruple overtime, two-point conversions will be employed thereafter.
Games may not end in a tie.
Instant replayCoaches are issued two challenges to request a review for all other plays. A third challenge is awarded if both are successful.
Plays during the final two minutes of each half and all overtime periods are subject only to booth review. All turnovers and plays ruled on the field to have scored points are automatically reviewed regardless of game time. Coaches are not allowed to challenge in either situation and may risk an unsportsmanlike conduct penalty if they attempt to do so; coaches cannot be disqualified on second unsportsmanlike.		Each coach receives only one challenge. If that challenge is successful, a second challenge is allowed.
All plays are subject to booth reviews.
Placement of ball following a touchbackFollowing kickoffs or free kicks after a safety: Receiving team's 25-yard line
All other touchback situations: 20-yard line of the team receiving possession		Same as NFL, except that a fair catch on a kickoff or free-kick after a safety between the receiving team's 25-yard line and the goal line is treated as a touchback, with the ball placed on the 25