Chess Ettiquette Regarding Unseen Check/checkmate?

[flobadob]

What is the correct etiquette in a chess game scenario whereby an opponents king is placed into check or checkmate, without either player noticing (ie perhaps a knight is involved). Then after another move is made the check/checkmate position is noticed, but because of the previous move an escape can be made.

Should the game then be brought back to the check/checkmate position, or just played out due to there being no check stated by the attacking player?

[Peter Pedant]

well I thougth you just crashed on

however there seems to be some debate:
goggle "unnoticed illegal moves in chess"

as far as I can see you agree beforehand what youre gonna do if this happens

In speed chess it definitely is ignored and you play on

[naomi24]

I don't know the 'correct' etiquette, but I'd say 'tough' - play on.

[Khandro]

The onus is on your opponent to indicate check, if it was mate, then obviously no move further would be possible anyway, if a check was unnoticed and play continued then the game would carry on.

[Buenchico]

There's no requirement, within the Laws of Chess, to declare 'Check'. (Indeed, at tournament level it's actually a breach of FIDE rule 12d to do so). So I'm of the opinion that the game should simply continue.

[magicmick]

Looking at the rules it says it is a illegal move to place your king into check, or to leave it in check. It then goes on to say if an illegal move has been made it should go back to the state of play before the move, this being check mate so game is then over.

[jim360]

The usual rule is that you try to reset the position to the one immediately before the illegal moves were made (in this case, everything after the check). Failing that, reset to an even earlier position. Failing that, then you should find an arbiter to decide what to do. In blitz games, illegal moves if noticed immediately can cost you the game, but only if there is no arbiter and if the opponent has sufficient material to win.

The current laws of chess seem to be a lot less harsh on illegal moves than used to be the case, when the player who'd made the illegal move was often obliged to move his king instead if possible; but the old rules say for the situation you describe that:

"If the King has been in check for several moves, and it cannot be ascertained how it occurred, the player whose King is in check must retract his last move and free his King from the check; but if the moves made subsequent to the check be known, they must be retracted."

While these rules are older, they are essentially the same as the modern ones and clearer on the case in point. No penalty; just retract to the last known legal position.

[flobadob]

Thanks for the thoughts. It appears that in friendly play the thought would be to play on. Chris, regarding rule 12d (yes, I Googled it), my reading of that would be that you should not talk of tactics related to the current game in play, rather than proclaiming check, or even general banter.

[Buenchico]

I'm probably not the best person to ask anyway, Flobby. I suspect that I was only given my Regional Coach award by the British Chess Federation because I put the course leader up at my house ;-)

[flobadob]

You and Bobby would be in good company lol