Questions tagged [illegal-move]

A move that doesn't respect the rules of chess.

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32
votes
3answers
13k views

Can a piece pinned to my king put the opponent's king in check?

I was playing a game with a friend online. A situation came up where he put me in check with his bishop, and I moved my rook to block it. His king was on the g file and my rook was on g2. The website ...
4
votes
3answers
14k views

Moving king into check

Can a player move their king into check if the opponents piece that is able to take king, is putting opponents king in check?
27
votes
2answers
22k views

I made an illegal move. What happens?

Especially in blitz or bullet games, it is possible that a player makes an illegal move, for example castles through check. If the opponent does notice the illegal move, then as far as I know the ...
16
votes
5answers
4k views

How to know when a FEN position is legal?

I am doing a personal project, where at one point I need to validate the FEN position, I started with some basics checks, such as check if there are kings and making sure there aren't any extra rows ...
19
votes
6answers
3k views

Are there any illegal positions that are difficult to spot?

I have a question and I'm sorry if it sounds very uninformed, I'm not a professional chess player so my interest is mere curiosity. I was wondering if there are examples of illegal positions that ...
7
votes
1answer
530 views

Illegal Move Missed — Too Late?

Standard game, USCF rules (if FIDE is different, I'd like to know). One side makes an illegal move -- specifically, castling through check. Neither player notices. Five moves later, the same side ...
21
votes
4answers
27k views

Why is castling through and out of check prohibited?

Why is castling disallowed when the king is in check or when the square the rook will be placed on is under attack? What is the rationale behind this ruling?
5
votes
2answers
903 views

Detect pinned pieces code

This post is a follow up of this one: C++ vs Java Engine move generation performance My goal here is to improve the performance of my move generator, which finishes perft (start_pos, 6) in 8.5 secs. ...
1
vote
2answers
164 views

In a tournament game, what should a player do if he find that his opponent's position is impossible, which was caused by an earlier illegal move? [duplicate]

For example, if a player realises that his opponent has two bishops of the same colour after a certain legal move (and assuming that it is clearly not caused by any pawn promotion), which implies that ...