The rule against intentional grounding seems to date from 1914, two seasons after an incomplete pass ceased to result in a turnover, in the period of rule experimentation that followed legalization of the forward pass in 1906.
Elements
A ball carrier, in any location, commits intentional grounding when throwing a pass with no realistic chance of completion in order to avoid a sack; for instance, throwing the football down near himself. However, the rules explicitly allow the quarterback to spike the ball immediately after receiving it from the center to stop the clock without using a time out. Intentional grounding is called only if all of the following components are present:
Imminent pressure: The passer must face "imminent loss of yardage." There is no violation when the passer is not about to be tackled but the receiver simply fails to run the route the quarterback expects.
Location: In the NFL and college, the quarterback must be inside the tackle box, the area between the two offensive tackles on the line. If the quarterback scrambles to either side and is closer to the sideline than that side's tackle lined up, there is no penalty. The NFL added this element of the rule in 1993 in order to protect quarterbacks, but high school football did not. However, intentional grounding can be called on a quarterback outside the pocket if the pass fails to go beyond the line of scrimmage. In the CFL, the quarterback is not subject to an intentional grounding penalty regardless of his location, so long as the pass reaches the line of scrimmage.
Target of the pass: The ball must be passed where there is no eligible receiver, such as well out of bounds. If a receiver is nearby but fails to catch the ball, or if a defender deflects the pass, there is no penalty.
After a flag is thrown, the officials may confer to decide whether all these components were present, and may "pick up the flag" upon finding there was no intentional grounding.
Penalty
The penalty for intentional grounding has several components so that the offense gains no benefit from the violation:
The offense is penalized 10 yards from the line of scrimmage, or to the spot of the pass if that is less advantageous.
The offense loses the down rather than replaying the down, as is the case for most other penalties.
If the quarterback threw the pass from his team's own end zone, the penalty results in a safety being scored by the defense.
Like many offensive penalties, intentional grounding committed near the end of either half results in a ten-second runoff of the game clock, if the defense desires. This ensures that intentional grounding is not an effective means of clock management.
