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King Capture Explanation Wanted

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chrisk17123

I thought I understood the rules around king capture but I just played a game where both myself and a 2300 thought incorrectly. 

Below is the game on move 13.b it will not allow king capture.  Can someone explain why? Is it somehow because of the yellow queen?

https://www.chess.com/variants/4-player-chess/game/28360034/48/4

 

I also think that they may have changed the rules since I went back to an old game where there was a possible mate that wouldn't work (at the time) due to a king capture superseding a checkmate.  When I went back to the analysis board today it now says that the checkmate would've won.

Can anyone explain this?

Thanks

Darksquareman

If You take yellows king red will take yours.

Darksquareman

Therefore taking yellows king is illegal.

chrisk17123

I think that in teams taking a king has priority over a check or checkmate.  See below from analysis board where green can legally take red king despite check so I don't think it's the red knight causing the issue.

Typewriter44

Simply put, you can't make a move that leaves you in check. If red had played Ne6+ instead of a double check, you'd be able to take the yellow king. 

EDIT: Just saw your previous comment. I think it's a bug

rojitto

I never saw this before, i tried to take the king and i couldnt because its a double check from red and yellow. If blue is checked by only one side, it allows the king capture. So maybe double check is more important than a king capture? I dont think so, it may be a bug

chrisk17123

I think the key is the double check, but I'm pretty sure that this is a bug or an unannounced rule change, since I'm pretty sure I have seen a scenario in the past involving double check (even a checkmate) where the king could still be taken.

I tried on analysis board and here are 2 examples where the only difference is c6 pawn making it single vs double check.  In the first screen, red can take king, second, red cannot take king:

 

Darksquareman

Lol sorry, didnt realize this was teams. I think you should be able to capture yellows king - unless, like rojo said, it has something to do with the double check.

Darksquareman

Wait but if both pieces that are double-checking you are the same color, then you cannot capture their king? This should be fixed.

JkCheeseChess

This is crazy...time to report it to spacebar!

To me, it makes 100% sense that if you are allowed to capture a king, you should be able to (doesn't apply to FFA since in teams, both teammates lose whereas in FFA only one loses and the other player can still be attacking your king). The double-check taking priority over the king capture is definitely a bug.

spacebar

I agree it's a bug.

Darksquareman

Imagine if a situation like this happened in a world championship.

spacebar

Actually now I remember.

The logic is that capturing the Y king does not eliminate the check from Red, hence it's not a legal move. The idea when we legalized king captures was that you could eliminate the threat to your king by eliminating the player and hence his pieces.

This makes sense in FFA. In teams too, I guess it's just a matter of definition, what rules we want. I remember already discussing this in the forum and we decided on the current implementation.

JkCheeseChess
spacebar wrote:

Actually now I remember.

The logic is that capturing the Y king does not eliminate the check from Red, hence it's not a legal move. The idea when we legalized king captures was that you could eliminate the threat to your king by eliminating the player and hence his pieces.

This makes sense in FFA. In teams too, I guess it's just a matter of definition, what rules we want. I remember already discussing this in the forum and we decided on the current implementation.

What about the situation where you capture blue's king and both of his pieces are eliminated along with the rest of his army?

JkCheeseChess

I tried it for myself using a legal position that you can reach in under 5 moves.

PGN4:

[Variant "Teams"]
[RuleVariants "EnPassant"]
[CurrentMove "14"]

1. g2-g4 .. Na5-c4 .. h13-h12 .. Nn5-l6
2. Qg1-g3 .. Nc4xd2 .. Bi14xb7 .. Nl6-k4
3. Qg3-c7 .. Nd2-e4 .. Nj14-i12 .. Nk4-l6
4. k2-k4 .. Ne4xf2+

Position:

If the yellow bishop moves anywhere along the a8-h1 diagonal (including capturing blue's queen), then red is under only one check and the next move can capture blue's king. However, if the yellow bishop moves along the opposite diagonal, for some reason, red is no longer allowed to capture blue's king, which I assume has to do with the double check mechanic. This does not make sense as:

1. This is teams, so whichever team gets their king captured first should technically lose, by the rules of the game (it just ends with checkmate in regular chess because you're obviously going to capture the king next move, but in teams some checkmates are impossible because the checkmated player's teammate can stop the mate the move after the checkmate and it's a longer story blah blah blah)

2. Even if it was FFA, red should still be allowed to eliminate blue because only blue's pieces are delivering the double check on red's king. To prove that it doesn't work in FFA either, I replaced the yellow bishop with a knight (because the bishop would be checking red's king in FFA). Here is the PGN4:

[StartFen4 "Y-0,0,0,0-1,1,1,1-1,1,1,1-0,0,0,0-0-{'enPassant'sad.png'k3:k4','','','')}-x,x,x,yR,yN,yB,yK,yQ,2,yR,x,x,x/x,x,x,yP,yP,yP,yP,1,yP,yP,yP,x,x,x/x,x,x,4,yP,yN,2,x,x,x/bR,bP,10,gP,gR/bN,bP,10,gP,gN/bB,bP,10,gP,gB/bQ,bP,10,gP,gK/bK,yN,rQ,9,gP,gQ/bB,bP,9,gN,gP,gB/1,bP,10,gP,1/bR,bP,4,rP,3,rP,1,gP,gR/x,x,x,8,x,x,x/x,x,x,1,rP,bN,1,rP,rP,rP,1,x,x,x/x,x,x,rR,rN,rB,1,rK,rB,rN,rR,x,x,x"]
[Variant "FFA"]
[RuleVariants "DeadKingWalking EnPassant"]
[CurrentMove "0"]

You can test both of these out for yourself: king captures are simply not allowed even if the double check is delivered by the same person, which I think, at the very least, is a bug that needs fixing.

spacebar

I agree and when in doublecheck from the same player it's def a bug. I've also found what's causing the trouble. I think it is in fact just a bug, and this behavior was only intended for FFA, so I'll fix it.