In chess, a fork is a tactic whereby a single piece makes two or more direct attacks simultaneously. Most commonly two pieces are threatened, which is also sometimes called a . The attacker usually aims to gain by one of the opponent's pieces. The defender often finds it difficult to counter two or more threats in a single move. The attacking piece is called the forking piece; the pieces attacked are said to be forked. A piece that is defended can still be said to be forked if the forking piece has a lower value. Besides attacking pieces, a target of a fork can be a direct mating threat. Or a target can be an implied threat. Forks are often used as part of a combination which may involve other types of chess tactics as well.
Forking piece
The type of fork is named after the type of forking piece. For example, a knight fork is a knight move that attacks two or more enemy pieces simultaneously. Any type of piece can perform a fork—including the king—and any type of piece can be forked. A fork is most effective when it is, such as when the king is put in check. The knight is the quintessential forking piece; in fact, some sources only use the term "fork" when a knight is the attacker, while if another piece is the attacker the tactic is called a or similar. A knight fork is powerful in several ways. The piece's unique L-shaped move allows it to attack any other type of piece without being threatened back by its targets, in seven different directions. Another advantage of the knight in forking is the ability to jump over any piece freely. The queen is also often used to fork, but since the queen is usually more valuable than the pieces it attacks, this typically gains material only when the pieces attacked are undefended or if one of them is the king and the other is undefended. The possibility of a queen fork is a very real threat when the queen is in the open, as is often the case in endgames. If a player wants to force an exchange of queens, forking the enemy queen and king with a protected queen can be useful. Pawns other than rook pawns can also be used to fork by attacking two enemy pieces diagonally—one to the left, the other to the right. Forks made by the king are an important consideration in endgame, where the king's ability to attack multiple pieces at once affects where a pawn's defenders can be safely placed.
In the Two Knights Defense after 4.Nc3, Black can eliminate White's e4-pawn immediately with due to the fork trick regaining either the bishop or the knight.
Escaping forks
Forks can possibly be escaped. A forked piece such as the queen might check the enemy king, giving time to move the second forked piece to safety on the next move.
Other terms
A fork of the king and queen, the highest material-gaining fork possible, is sometimes called a royal fork. A fork of the enemy king, queen, and one rooks is sometimes called a grand fork. A knight fork of the enemy king, queen, and possibly other pieces is sometimes called a family fork or family check.
