In short: The little flag on an analog chess clock that falls when the time is up. Saying the flag has fallen means the player's time has run out, on a digital clock too.
Also called flag fall.
An analog chess clock has a little flag on each clock face. It falls at the very moment the player's time runs out. A digital clock has no flag that falls, but the expression has stayed: the flag has fallen means the time is up.
Losing on time
If a player doesn't make their moves within the allotted time, the game is lost for that player. The flag counts as fallen when the arbiter sees it, or when one of the players makes a valid claim.
The most famous example may be Hastings 1895. Wilhelm Steinitz had launched an attack that Curt von Bardeleben could not meet. Von Bardeleben never resigned. He left the board and let his time run out.
See the whole game: Steinitz–von Bardeleben 1895. Another example is Stoltz–Steiner 1952, where Herman Steiner's time ran out after 34. Rxf6: Stoltz–Steiner 1952.
The exception: when your opponent can't mate
If your time runs out, the game is still drawn if your opponent can't checkmate you by any possible series of legal moves. It isn't enough for your opponent to stand much better. What matters is whether a mate is possible at all.
It can also go the other way. The player with more material can lose on time against a lone pawn, because the pawn could become a queen and a mate is then possible, however unlikely.
In blitz and rapid, when no arbiter is watching every game, you may stop the clock yourself and call the arbiter when your opponent's flag has fallen. Even then it is a draw if you can't checkmate in any way. More about time under time control.
Frequently asked questions
Do you always lose when your time runs out?
No. If your opponent can't checkmate you by any possible series of legal moves, the game is drawn instead.
Who says that a flag has fallen?
A flag counts as fallen when the arbiter sees it, or when one of the players makes a valid claim.
Updated November 14, 2026