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You can make illegal moves in over the board chess, and sometimes it's advantageous to do so. E.g. In blitz chess an invalid move is an immediate loss. So, if

You can make illegal moves in over the board chess, and sometimes it's advantageous to do so. E.g. In blitz chess an invalid move is an immediate loss. So, if you're going to lose anyway, you can make an invalid move hoping your opponent doesn't take the time to notice. One common one is to move your king next to your opponent's king, putting their king in check, if they don't call you on it, and don't move their king out of check, they lose. Unofficially, this is considered part of the game in blitz, but is considered unsportsmanlike in long games (where it's not an immediate loss).

distortedsignal 4y ago
Is that... true? Are there tournament rules that say that? I'm not much of an OTB player, but this strikes me as somewhat against the spirit of the game. I will freely admit that I don't play blitz unless it's on a computer (I hate chess clocks) and computers don't allow illegal moves, but I would be very surprised if tournaments operated like this. Even small, local tournaments.
- kanzenryu2 4y ago
  I remember reading about a serious tournament game where somebody castled twice. Nobody noticed during the game. I wonder how many computer databases allow that game to be entered.
  - Someone 4y ago
    That must have been Heidenfeld - Kerins, Dublin 1973. https://www.chessgames.com/perl/chessgame?gid=2024861 https://www.chessgames.com/perl/chessgame?gid=2024861. White castled short on move 10 and long on move 33. That didn’t help, though. White lost the game. Also, it seems that site’s software doesn’t allow entering the full game.
- crdrost 4y ago
  Longer games go by FIDE's "Laws of Chess" which has a section 7 called "Irregularities" that indeed specifies the behavior if you accidentally knock over pieces or the game board falls over or you make an illegal move (moving away a piece that was keeping you from check etc). Resolving irregularities does require your opponent to notice the irregularity and bring it to the attention of the referee. Not sure about Blitz.
deleted 4y ago
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kanzenryu2 4y ago
From memory it wasn't so long ago that the laws of chess "allowed" you to play an illegal move to cause a checkmate (e.g. Qd1xf7 mate). Your opponent would say "hey that's an illegal move, take it back". You could then say "according to this rule, taking back illegal moves can only be done during a game, and according to this other rule, checkmate immediately ends the game". Note that it can be discovered during a game that a move several turns ago was actually illegal, and the board should be returned to that position (and times adjusted). I had this happen to me once.
- shuntress 4y ago
  The "checkmate immediately ends the game" rule gets really weird in 3-chess.
- gmiller123456 4y ago
  As a former USCF tournament director, I can say this is not true. Rule 13A - "The player who checkmates the opponent king, providing the mating move is legal, wins the game." Additionally, there are many contradictory rules that can't all be applied, so there is a lot of room for the tournament director to apply the rules according to the spirit of the game rather than the word of the law.

distortedsignal 4y ago

Is that... true? Are there tournament rules that say that? I'm not much of an OTB player, but this strikes me as somewhat against the spirit of the game. I will freely admit that I don't play blitz unless it's on a computer (I hate chess clocks) and computers don't allow illegal moves, but I would be very surprised if tournaments operated like this. Even small, local tournaments.

kanzenryu2 4y ago
I remember reading about a serious tournament game where somebody castled twice. Nobody noticed during the game. I wonder how many computer databases allow that game to be entered.
- Someone 4y ago
  That must have been Heidenfeld - Kerins, Dublin 1973. https://www.chessgames.com/perl/chessgame?gid=2024861 https://www.chessgames.com/perl/chessgame?gid=2024861. White castled short on move 10 and long on move 33. That didn’t help, though. White lost the game. Also, it seems that site’s software doesn’t allow entering the full game.
crdrost 4y ago
Longer games go by FIDE's "Laws of Chess" which has a section 7 called "Irregularities" that indeed specifies the behavior if you accidentally knock over pieces or the game board falls over or you make an illegal move (moving away a piece that was keeping you from check etc). Resolving irregularities does require your opponent to notice the irregularity and bring it to the attention of the referee. Not sure about Blitz.

deleted 4y ago

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kanzenryu2 4y ago

From memory it wasn't so long ago that the laws of chess "allowed" you to play an illegal move to cause a checkmate (e.g. Qd1xf7 mate). Your opponent would say "hey that's an illegal move, take it back". You could then say "according to this rule, taking back illegal moves can only be done during a game, and according to this other rule, checkmate immediately ends the game". Note that it can be discovered during a game that a move several turns ago was actually illegal, and the board should be returned to that position (and times adjusted). I had this happen to me once.

shuntress 4y ago
The "checkmate immediately ends the game" rule gets really weird in 3-chess.
gmiller123456 4y ago
As a former USCF tournament director, I can say this is not true. Rule 13A - "The player who checkmates the opponent king, providing the mating move is legal, wins the game." Additionally, there are many contradictory rules that can't all be applied, so there is a lot of room for the tournament director to apply the rules according to the spirit of the game rather than the word of the law.