A fork is a move that attacks two or more enemy pieces at the same time with one piece. Because only one target can be saved per move, a fork usually wins material. Knights are the most famous forkers, but every piece — even the king and pawns — can fork.
The fork is the first real tactic most players learn, and it never stops appearing — from beginner games to world championship matches. One piece, two targets, one move to respond. Something falls.
The classic: a knight lands on f7 in a castled-kingside position gone wrong, attacking the queen on d8 and the rook on h8 simultaneously. The queen steps away, the knight takes the rook. Three points of material, courtesy of one jump.
Knights are the archetypal forking piece for a reason: their attack pattern is non-linear, so their targets never see the threat along a line they were watching. A knight fork that hits king and queen at once — the royal fork — is among the most devastating single moves in chess.
But every piece forks. A pawn push that attacks two pieces on adjacent diagonals. A queen check that also eyes an undefended rook across the board. Even a king, in the endgame, stepping between two loose minor pieces.
Look at the anatomy: a fork wins material only if the targets can't both be saved. That usually requires at least one target to be either loose — undefended, so capturing it costs nothing — or more valuable than the forking piece, like a king or queen. This is why keeping your pieces defended is such effective tactical insurance: against a well-coordinated position, most fork attempts simply don't win anything.
Forks also frequently arrive with tempo, as a check. A check-and-fork gives the defender no time for counter-tricks: the king must be attended to first. When calculating whether a fork works, always check whether the defender has an in-between resource — a zwischenzug — such as a counter-check or a bigger threat elsewhere.
Two scans cover most cases. First, know your opponent's knight-jump squares: any square a knight can reach that touches two of your pieces is a live threat. Second, track your loose pieces — forks feed on undefended targets.
Most players who lose to forks lose to the same kind of fork repeatedly. Chessdock finds the forks you missed and the ones you walked into across your own games, and turns them into puzzles until the pattern is burned in.