Side to move

The side to move is the player whose turn it is to make the next legal move. White moves first, and the turns then alternate. A player has the move once the opponent's move has been made under the rules.

The turn is part of the position, not merely a practical reminder. The same arrangement may be checkmate, where the king is attacked and no legal reply exists, or stalemate, where no legal move exists but the king is not in check, depending on who must move. It also changes which captures and threats can be carried out immediately.

For that reason, visually identical boards are not the same position for repetition if a different color has the move. Chess programs and position formats store this fact explicitly alongside the pieces and certain special rights.

Normally, the running clock belongs to the side to move because the opponent starts it when they press the clock. The turn, however, is defined by the game state, not solely by a clock that was operated incorrectly or is defective.