What is your judgement if you are the arbiter?

I came across a tournament with this scenario.

Player A was playing against player B in a rapid tournament. When they reached endgame of a same color bishop(dark square), and several pawns in a drawing position, player B made move that the bishop end up in white square. After 3 moves, player A only noticed the player B's bishop in different color when his pawn was captured. Thus, player A called for arbiter. The arbiter in charge also saw the same color bishop endgame before the dispute happens. When question further, player B denied that his pawn is a dark square bishop but had to admit later on, that, when there were eye witness (arbiter and appeal committee).

A player that was in the appeal committee saw that the player B's bishop was originally a dark square. 

What would your decision be? Any experienced arbiters here?

B should lose the game immediately and be suspended from further play for some period.

Is there any FIDE laws on that? Would love to hear from more ppl here, esp arbiters, if there is any here/

Of course there are. You can read them on the FIDE website. https://www.fide.com/fide/handbook.html?id=208&view=article

This could be a tough decision.

Based solely on the posted info I would rule player A wins the game.

I would make that ruling based on article 12 of bringing the game into disrepute.

I would think in this case article 12 is more relevant than simply article 7 for ordinary illegal moves.

I think the evidence suggests that the illegal move was intentional and warrants stronger penalties than normal illegal moves.

I read about this. With the player B denying his Bishop to be in a dark square, to me it shows that he did it intentionally. Thus article 7 doesn't mention on the player's misconduct.

Yes. The decision is tough. I wonder if there is a case that happen before same like this. If there is, at least there is a precedence to follow. 

Depends if he did it by accident or on purpose.

If he did it by accident, then the game should be backtracked to the last position you both remember.

If he did it on purpose, then he should forfeit the game and forfeit his place in the tournament too.

Got the answer from the top FIDE ppl.

Based on the Article 7.1 and 7.6, 

I was a U.S. Chess Federation Tournament Director (& Arbiter) and the rule, I think in FIDE also, is that:

1) no one besides Tournament Officials and the players can give testimony as to a position,

2) if the illegal move was made within the last 10 moves, then the last known legal position must be reestablished.  The rule says NO time is restored to the clocks, but there is some discretion allowed by USCF to Tournament Directors.  In my experience, I made sure each player had at least 2 minutes on their clocks (no increments back then) if I restored a previous position that was near the endgame, 3 minutes if it was in a game with lots of pieces still on the board, adding the same amount of time to each clock.

3) if the illegal move was made prior to each player's last 10 moves or if the players' scoresheets were kept so poorly the last position before the legal position couldn't be agreed to, the game will stand with the illegal move and with no time adjustment.

Note: If one player has recorded the game properly and the other hasn't, the player with the proper record's scoresheet is used to reestablished the game.  Unfortunately, I have observed cases where a veteran notices that a newbie opponent isn't properly keeping score and the veteran then makes up and records moves that would give him a winning position and "accidentally" knocks the pieces off the board.  I was supposed to follow the USCF rule going by the veteran players scoresheet, but -dealing mostly with teenagers- I always moved the pieces back to where both players said the board was where the game was.

I came across this interesting thread. But the rule interpretations have been made for a standard game, not a rapid game! I add the description for the rapid game per my understanding below. Please check and let me know if anything is wrong.

Assuming the tournament was played according to FIDE rules, then "Appendix A. Rapid chess" in the FIDE rules apply. If there is "adequate supervision", then the competition rules apply, so the rules for standard chess. Otherwise specific rules formulated under this appendix apply. So first the following must be checked:

"Appendix A. Rapid chess
A.3.1 The Competition Rules shall apply if:
A.3.1.1 one arbiter supervises at most three games and
A.3.1.2 each game is recorded by the arbiter or his assistant and, if possible, by electronic means."

"Competition Rules" are the rules for standard games. So if this situation applies, informally, the last known position before the illegal move must be reinstated.

Otherwise, if there is no "adequate supervision", the rules stated after "A.4 Otherwise the following apply: " are used. The following rule is relevant for the example:

"A.4.2 If the arbiter observes an action taken under Article 7.5.1, 7.5.2, 7.5.3 or 7.5.4, he shall act according to Article 7.5.5, provided the opponent has not made his next move. If the arbiter does not intervene, the opponent is entitled to claim, provided the opponent has not made his next move. If the opponent does not claim and the arbiter does not intervene, the illegal move shall stand and the game shall continue. Once the opponent has made his next move, an illegal move cannot be corrected unless this is agreed by the players without intervention of the arbiter."

For the situation, this means that the move stands, including that the arbiters previously observed that it was a black bishop. This is not enough. He needs to observe the illegal move itself to intervene, for this case. The observation might, however, be relevant for an appeal.

As the arbiter had to be called, it seems the game was not under "adequate supervision", so the second case above would apply.

It is very important that the player makes an appeal if assuming appropriate. Without an appeal, FIDE will take no action. However, the illegal move stands, no matter what. There is a rule, however which can overrule. The appeal committee based on "Article 11: The conduct of the players", then "11.1 The players shall take no action that will bring the game of chess into disrepute." then "11.6 Infraction of any part of Articles 11.1 - 11.5 shall lead to penalties in accordance with Article 12.9". Penalties are for example to declare the game lost for player B.

By the description, it is not clear, if an "overrule" would be appropriate. That would be a per case decision of the appeals committee, depending on the circumstances. Please let me know should there be any other understanding.

I wanted to point out; the question is about Rapid Chess, not Standard Chess.

The FIDE rules for Rapid chess (for details, check the wording in the rules) say the following:

When there is at least one arbiter or three games, and the game is recorded. In this case, when an illegal position is found, assuming that it is really clear, then "the game shall continue from the last identifiable position prior to the irregularity". The arbiter can impose a penalty.

Otherwise, when the illegal move is not immediately claimed it stands.

In both cases, even if it can be proven that an illegal move was performed, it does not count to the two illegal moves loses the game. For that, it must immediately be claimed.

In the case when player A makes an appeal, and it can be proven that there was an illegal move by player B, the move still stands. By the rules, the committee, however, has the possibility to make an assessment, if player B brings the game into disrepute with his actions. That is sort of a rule to overrule everything else, for unseen situations. In this case, they can also declare a win for player A.

The situation here at first is that the illegal move was not immediately recognized but is logically deduced. That is a problem. One should not fix on the idea, that the only possibility for the bishop now on the white square is that player B has moved it to a white square. For example, it could also theoretically be that player B made an imprecise movement with the bishop. Then player A adjusted the bishop by accident to the white square.

In other words as long that player B did not say that he made an illegal move or there is video footage or other really clear evidence, this is not enough to accuse player B. The logical deduction; the black bishop was on the black square, now it is on a white square, so the only possibility is, that player B made an illegal move is incorrect.

If that is clear, during the game the position should have to be reinstated (for that also the recording was required) if "enough supervision". Otherwise, the game would have continued. When appealed, the decision on the appeal committee would be on a per case basis; there is no specific rule for this case.