Illegal-move penalty

An illegal move may move a piece in a forbidden way, leave the player’s own king in check, meaning under attack, or break another essential condition. Under standard international competition rules, the specific penalty is triggered when the illegal move becomes a completed move, normally when the player presses the clock.

Standard competitive procedure

1. The position immediately before the irregularity, meaning the rules problem, is restored. If it cannot be determined, play resumes from the latest earlier position that can be identified.
2. For the player’s first completed illegal move, the opponent receives two extra minutes.
3. For the same player’s second completed illegal move, that player loses. The result is a draw if the opponent could not deliver checkmate, an attack on the king with no legal response, through any possible series of legal moves.

That final exception depends on whether mate is possible in the actual position, not on a simplified piece list. Mating material, meaning the pieces and circumstances that would allow some legal mating sequence, must therefore be evaluated in the actual position.

Rapid chess, a shorter form of play than standard chess, changes some numbers and procedures. Under the international rapid appendix, two-minute penalties become one minute, and under some supervision conditions an illegal move must be claimed or corrected before the opponent makes the next move. The event regulations and supervision system therefore matter.