Flagging

Flagging is the common term for making the opponent run out of time, normally with the aim of winning the game. The name comes from analog chess clocks, where a small flag falls when the allotted time expires. In fast online chess it is also used as a verb: to flag someone means to play with the goal of making their clock hit zero before yours.

The board position still matters. Under the Laws of Chess of the International Chess Federation (FIDE), a player who runs out of time normally loses, but the game is drawn if the opponent could not checkmate by any possible sequence of legal moves. Running out of time therefore does not automatically guarantee the other player a win in every position.

Flagging is especially visible in blitz and bullet, formats with very little time per player, where fractions of a second can decide the game. A player may simplify decisions, choose easy-to-execute moves, or use a premove, a move entered before the opponent completes their move, to save time. That speed also increases the risk of a mouse slip, an accidental move caused by mouse or touchscreen input.