The touch-move rule in chess states that a player who intentionally touches one of their own pieces must move it, and if they touch an opponent’s piece, they must capture it — provided the capture is legal.
This rule applies as soon as contact is deliberate. If a player accidentally brushes a piece, they may say "j’adoube" (French for "I adjust") before touching it, to signal they only wish to reposition the piece on its square without being obligated to move it. Crucially, this declaration must be made before touching the piece, never after.
In practice, the touch-move rule carries significant consequences: a player who hesitates and reaches for a piece before deciding on their move may be forced to play a disadvantageous move. It is therefore essential to have mentally committed to a move before reaching for any piece on the board.