Questions tagged [illegal-move]

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

Filter by
Sorted by
Tagged with
54 votes
3 answers

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 ...
ken's user avatar
  • 551
43 votes
2 answers

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 ...
Armen Tsirunyan's user avatar
4 votes
3 answers

Moving king into check [duplicate]

Can a player move their king into check if the opponents piece that is able to take king, is putting opponents king in check?
G Foster's user avatar
22 votes
1 answer

Why is it illegal to move into check?

In chess, it is against the rules to move into check, or to not move out of check. But why? Obviously, if you went against this rule, you'd immediately lose. But it seems strange to make it illegal to ...
Winston Ewert's user avatar
36 votes
2 answers

Is taking the opponent's king an illegal move?

In competition blitz games, making an illegal move and then pressing the clock forfeits the game if the opponent claims the illegal move as long as they do not make a new move, as a new move would ...
Pep's user avatar
  • 1,354
27 votes
4 answers

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?
Alexandros's user avatar
23 votes
7 answers

How do you know when a FEN position is legal?

I am making a research on validating FEN positions, at first it is obvious the basics things to look for, such as checking if there are only two kings and making sure the rows or columns add up and ...
ajax333221's user avatar
  • 3,138
8 votes
1 answer

Illegal Move Missed-Too Late?

This question is about standard games under USCF rules (if FIDE is different, I'd like to know). Say that one side makes an illegal move-specifically, castling through check. Neither player notices. ...
Steve Weber's user avatar
25 votes
6 answers

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 ...
seawalker's user avatar
  • 359
23 votes
1 answer

The illegal moves in Carlsen-Inarkiev

In the first round of the World Blitz Championship in Riyadh. Magnus Carlsen played Ernesto Inarkiev and the game ended strangely. [FEN ""] [StartPly "53"] [Event "World Blitz ...
user1583209's user avatar
  • 20.7k
7 votes
1 answer

Why isn't legal move filtering done at search time?

Most engines have some method of filtering out pseudo-legal moves from the actual legal ones. However, is there any reason not to keep them? With bit-boards, you can quickly filter out the ones that ...
AAce3's user avatar
  • 388
6 votes
2 answers

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. ...
Fernando's user avatar
  • 425
3 votes
1 answer

What happens if a player makes an illegal move and nobody notices?

What happens if a player makes an illegal move (i.e. a realistic case could be, he castles after he already moved the King), but none of the player notices, and the game goes on and on for a lot of ...
A. N. Other's user avatar
  • 6,816
2 votes
2 answers

USCF: Should the arbiter correct illegal moves without a player claim?

Should an USCF arbiter correct illegal moves without a player claim? Here is the USCF link: USCF rules of chess Here is the FIDE link: FIDE rules of chess USCF and FIDE rules are NOT 100% equal. What ...
Beginner's user avatar
  • 1,242
2 votes
2 answers

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 ...
Zuriel's user avatar
  • 8,819