Chess tactic


In chess, a tactic refers to a sequence of moves that limits the opponent's options and may result in tangible gain. Tactics are usually contrasted with strategy, in which advantages take longer to be realized, and the opponent is less constrained in responding.
The fundamental building blocks of tactics are move sequences in which the opponent is unable to respond to all threats, so the first player realizes an advantage. This includes forks, skewers, batteries, discovered attacks, undermining, overloading, deflection, pins, and interference. The Encyclopedia of Chess Middlegames gives the following tactics categories: Double Attack, Pawns Breakthrough, Blockade, Decoying, Discovered Attack, Passed Pawn, X-ray Attack, Interception, Deflection, Pin, Demolition of Pawns, Overloading, Annihilation of Defense, Pursuit, Intermediate Move, and Space Clearance.
Often tactics of more than one type are conjoined in a combination.

Attacking and defending pieces

A piece is said to attack an opponent's piece if, in the next move, it could capture that piece. A piece is said to defend a piece of the defender's color if, in case the defended piece were taken by the opponent, the defender could immediately recapture. Attacking a piece usually, but not always, forces the opponent to respond if the attacked piece is undefended, or if the attacking piece is of lower value than the one attacked.
When the piece attacked is a king, then a player has exactly three options:
When the piece attacked is not a king, a player has more options:
When a player is able to capture the opponent's piece without losing any of their own, the player is said to have "won "; i.e., the opponent will have fewer pieces remaining on the board. The goal of each basic tactic is to win material. At the professional level, often the mere threat of material loss induces the opponent to pursue an alternative line. In amateur games, however, tactics often come to full fruition – unforeseen by the opponent and resulting in material gain and a corresponding, perhaps decisive, advantage. Material gain can be achieved by several different types of tactics.

Discovered attack

A [|discovered attack] is a move which allows an attack by another piece. A piece is moved away so as to allow the attack of a friendly bishop, rook or queen on an enemy piece. If the attacked piece is the king, the situation is referred to as a discovered check. Discovered attacks are powerful since the moved piece may be able to pose a second threat.
A special case of a discovered check is a double check, where both the piece being unmasked and the piece being moved attack the enemy king. A double check always forces the opponent to move the king, since it is impossible to defend attacks from two directions in any other way.

Fork

A fork is a move that uses one piece to attack two or more of the opponent's pieces simultaneously, with the aim to achieve material advantage, since the opponent can counter only one of the threats. Knights are often used for forks, with their unique moving and jumping ability. A common situation is a knight played to c2 or c7, threatening both the enemy rook and king. Such forks checking a king are particularly effective, because the opponent is forced by the rules of chess to immediately remove the check to his king. The opponent cannot choose to defend the other piece, or use a zwischenzug to complicate the situation. Pawns can also be effective in forking. By moving a pawn forward, it can attack two pieces—one diagonally to the left, and another diagonally to the right.
The queen is also an excellent forking piece, since she can move in eight different directions. However, a queen fork is only useful if both pieces are undefended, or if one is undefended and the other is the enemy's king. The queen is the most valuable attacking piece, so it is usually not profitable for her to capture a defended piece.
Fork attacks can be either relative, or absolute. The targets of a fork do not have to be pieces, although this is known as a double attack. One or more of the targets can be a mate threat or implied threat.

Pin

A [|pin] is a move that inhibits an opponent piece from moving, because doing so would expose a more valuable piece behind it. Only bishops, rooks, and queens can perform a pin, since they can move more than one square in a straight line. If the pinned piece cannot move because doing so would produce check, the pin is called absolute. If moving the pinned piece would expose a non-king piece, the pin is called relative.

Skewer

A skewer is a move which attacks two pieces in a line, similar to a pin, except that the enemy piece of greater value is in front of the piece of lesser value. After the more valuable piece moves away, the lesser piece can be captured. Like pins, only queens, rooks, and bishops can perform the skewer, and skewer attacks can be either absolute or relative.

Pawns

Pawns are the least valuable chess piece, so are often used to capture defended pieces. A single pawn typically forces a more powerful piece, such as a rook or a knight, to retreat. The ability to fork two enemy pieces by advancing a pawn is often a threat. Or a simple pawn move can reveal a discovered attack. When pawns are arranged on a diagonal, with each pawn guarded by the pawn behind it, they form a wall or protecting any friendly pieces behind them. A weak pawn structure, with unprotected or isolated pawns ahead of more valuable pieces, can be a decisive weakness. A pawn that has advanced all the way to the opposite side of the board is promoted to any other piece except a king.

Sacrifices

A sacrifice of some material is often necessary to throw the opponent's position out of balance, potentially gaining positional advantage. The sacrificed material is sometimes later offset with a consequent material gain. Pawn sacrifices in the opening are known as gambits; they are usually not intended for material gain, but rather to achieve a more active position.
Direct attacks against the enemy king are often started by sacrifices. A common example is sacrificing a bishop on h2 or h7, checking the king, who usually must take the bishop. This allows the queen and knight to develop a fulminant attack.

Zugzwang

Zugzwang occurs when a player is forced to make an undesirable move. The player is put at a disadvantage because he would prefer to pass and make no move, but a move has to be made, all of which weaken his position. Situations involving zugzwang occur uncommonly, but when they do occur, it is almost always in the endgame, where there are fewer choices of available moves.

Zwischenzug

Zwischenzug is a common tactic in which a player under threat, instead of directly countering, introduces an even more devastating threat. The tactic often involves a new attack against the opponent's queen or king. The opponent then may be forced to address the new threat, abandoning the earlier attack.
The concept of a zwischenzug is often listed as a tactic, but might properly be called a counter-tactic instead. The effect of a zwischenzug is to change the status quo before a tactic can come to fruition. The near ubiquity of the zwischenzug makes long combinations all the more rare and impressive.