Just The Rules: Flag Falls, Part II

Tim Just is a National Tournament Director, FIDE National Arbiter, and editor of the 5th & 6th edition of the US Chess Rulebook. He is also the author of My Opponent is Eating a Doughnut & Just Law, which are both available from US Chess Sales and Amazon/Kindle. Additionally, Tim recently revised The Guide To Scholastic Chess, a guide created to help teachers and scholastic organizers who wish to begin, improve, or strengthen their school chess program. Tim is also a member of the US Chess Rules Committee and his new column exclusive to US Chess, “Just the Rules” will help clarify potentially confusing regulations.

There is tension in the air. A crowd is squeezed around your board. You and your opponent rush to make each move before one of you run out of time. BAM-BAM-BAM, you slam down your pieces while still managing to punch your clock. Your opponent has a few seconds left. Your time is even shorter. You are stalking their king. BAM, you checkmate your foe in an instant, and then your flag falls. Your adversary claims the checkmating move is incomplete. They contend you lost on time. They tell the TD you did not press your clock to prevent your flag from falling; therefore, you are out of time, and the checkmating move is unfinished. After all, they claim, to finish your move the rules say you have to press the clock. The TD denies the claim. You win the game. Why? Checkmate trumps everything if you can deliver it while it is still your move. At the instant the mating move is made, the game is over, and time stops.

Checkmate ends the game so there is no flag fall claim.

The instant the legal move is made that delivers checkmate, the game is over. Anything that takes place after that, like a flag fall, is immaterial.

Checkmate is final.

Of course, if you let your flag fall first and then make a mating move; you are out of time and out of luck. Your opponent may now make a legitimate flag fall claim. The rule of thumb is that whichever occurred first, the flag fall or the checkmate, determines how the contest ends. What happens if it can’t be determined which one took place first—the checkmate or the flag fall? Then the checkmate typically gets the nod.

Watch out for the times when you and your opponent are in time trouble and one of you delivers a legal checkmating move—but neither of you realize it—and you both play on. When this happens, and it changes the outcome of the game, get a TD; furthermore, discovering a game changing checkmate earlier in the game during a later post-mortem becomes problematical—especially if you, your opponent, and both your scoresheets disagree about the earlier mate. Or, perhaps you are both in full agreement about the earlier game ender. Either way, it is time for a visit to the TD.

Interestingly stalemate also instantly ends the game and stops the clock in the same way checkmate does.

For the claim to not be a bust, mating material is a must.

Your opponent has lots of time left. You have mere seconds. Your flag falls. You are out of time. Your opponent has only a king plus a lone bishop and claims a win on time. Your adversary would never be able to mate you with his material, even if there were no clock on the game. The game is a draw—and the board’s position isn’t considered when this rule is enforced. Only the material on the board is examined. A flag fall claim is linked to mating material. For an official list of material that makes mate impossible, see the rulebook. Interestingly a single pawn is regarded as mating material (you can trade up to a queen!).

An interesting game strategy used by some players: Your clock’s flag is about to announce that you lost. Your opponent has mating material. To change your pending zero into a half-point, simply capture enough of your adversary’s pieces so that they are left without mating material!? No mating material means no win on time for them.

A player’s fallen flag means they can’t brag.

This seems kind of obvious, but you need to have time left on your clock (your flag can’t have fallen) before you claim that your opponent is out of time.

If both flags are down in the last (or only) time control—and there are no game ending claims pending before the flags fell—then the contest is a draw.

The next few postings will take a journey through the maze of drawing regulations.

Browse all of Tim Just’s articles here. 


  1. Very well written article on flag fall Tim. I had a game last night I was watching as one player was in severe time pressure. Both players have plenty of material on the board so black is sweating this one (as he is in serious time trouble). Black’s flag falls. The players around me looked at me as if I were going to call the flag fall (No!). White looks up at me but does not claim anything and I just stand there impassively watching and saying nothing. Now a twist in the game. Black makes his next move, presses the clock, and both clock’s roll over into sudden death. Unfortunately the clock’s rolled over on move 20. Time control is 40/90;sd/30;d/5. Now I have to step in for an erroneously set clock. I make white the owner of the clock properly set the clocks and give two extra minutes to black (penalizing white). White still had not claimed a win on time (that is white’s responsibility not mine). A crowd is watching now as if I’m running a strange chess tournament. Black does finally realize he had flagged and now has the 2 minutes I added as a penalty to white to reach 40 moves and blitzes away. They both make the 40 moves and go into sudden death where black once again flags. This time white finally does exclaim “your flag has fallen”. I explain the rules once again to everyone that flag falls are called by players only. White says “whew I got lucky”. I told him no you won a long time ago but never claimed the flag fall and then you received a 2 minute penalty for having an improperly set clock which allowed the game to continue. I’m sure he will permanently remember that for the future.

  2. Tim wrote:
    Checkmate trumps everything if you can deliver it while it is still your move. At the instant the mating move is made, the game is over, and time stops.

    Checkmate ends the game so there is no flag fall claim.

    The instant the legal move is made that delivers checkmate, the game is over. Anything that takes place after that, like a flag fall, is immaterial.

    A correctly called Flag Fall also instantly ends the game, even if one second later the losing player physically moves his rook to deliver an apparent checkmate.

    The arbiter is called over, and the only physical proof he can see is the checkmate on the board. There is no physical proof that the mated player correctly called Flag Fall one second before the mate move. So the checkmate will be given the benefit of the doubt, inappropriately.

    Much better to require the checkmating player to press his clock one final time after achieving mate (or to at least pause both clocks), to preserve physical proof that the mate was delivered before time expired.
    Thus it is illogical that the USCF intentionally rejects a rule change to require this final clock press.

    The argument – “Yeah, but checkmate ends the game” – is just an obfuscated way of saying – “We don’t feel like requiring the final clock press, despite the potential problem”.
    Obviously checkmate has always meant the end of the game, dating back to 1475 or earlier. But the ‘checkmate ends the game’ *ethos* that the current rule leans on is no older than the widespread adoption of the chess clock.

    Thank you.

  3. The 2014 Arbiters’ Manual includes this statement in an explanatory box associated with Competition Rule 6.11: “If digital clocks are used, it is possible to define which flag has fallen first.” In a situation where both flags have fallen, can you tell me how a digital clock distinguishes which flag fell first? Thank you!

  4. I guess you would have to check the notation on the scoresheets. Whoever moved last (according to notation) wins the game by virtue of the fact that all scoresheets are recorded perfectly. Therefore playing over all games in chess where both flags are down proves who won the game:):)

  5. That would be true of any clock. The FIDE rule states that there is some difference between digital and analogue clocks. The implication is that the clock itself indicates whose clock fell first. The DGT North American does this if it is set for some time controls but not for others. For a single time control without a delay or increment, both clocks can expire (showing 0.00) but a flag icon is displayed only for the clock whose flag fell first. The irony is that the Competition Rule 6.11 quoted above has been deleted from the 2018 FIDE Laws of Chess. Instead there is a rule that says “In the case of a time control being passed, a sign on the display must signal clearly which player passed the time control first. …” (FIDE Handbook, C. General Rules …, 02. Standards of Chess Equipment, … Article 5: Chess clocks, paragraph I presume that clocks used elsewhere than in the US can do this.

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