A fork is a tactical device in which one piece attacks two (or more) enemy pieces at once. It is usually impossible to defend both in one move, so one of them is lost.
Any piece can fork, but the term is most often used for the knight and the pawn.
The knight fork
The knight attacks “over heads” and from unexpected squares, which makes its forks especially treacherous. The most dangerous is a fork with check: the opponent has to get out of check, and the second piece is lost.
A knight fork of king and queen is called a “royal fork” — losing the queen usually decides the game.
The pawn fork
A pawn is worth less than any piece, so its fork almost always wins material: any piece it attacks is worth more than a pawn.
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How to find forks
- Look at the opponent's undefended pieces and at pieces standing on the same line or a knight's move apart.
- Look for squares from which your piece attacks two targets — especially knight squares near the opponent's king and queen.
- Remember: a fork is often prepared by a sacrifice that forces the opponent's pieces onto “forkable” squares.
The fork is a special case of the double attack.