Questions tagged [illegal-move]

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

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34
votes
2answers
19k views

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 he does not make a new move, as a new move would ...
33
votes
3answers
15k 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 ...
29
votes
2answers
27k 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 ...
22
votes
4answers
29k 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?
21
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 ...
20
votes
1answer
10k views

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 ...
19
votes
6answers
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
1answer
4k views

Carlsen - Inarkiev game illegal moves

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 Championship"] [Site "...
10
votes
2answers
1k views

What “double moves” are sometimes considered legal?

As we know, castling is a legal "double move," where two pieces are moved at once. But in my country, Indonesia, in my childhood, the opening below was an 'assumed legal' double move to counter 1.e4 ...
9
votes
2answers
1k views

Touch a piece and then claim opponent's previous move was illegal

In a last round tie between 2 players fighting for top seed in a competition, here is what happened. White had 18 seconds on his clock and black had 26 seconds. Black was winning. At move 56, black ...
8
votes
1answer
821 views

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. ...
7
votes
3answers
4k views

Can a king be checked with another king when checking square is protected by the side which gives the check? [duplicate]

Can a white King move next to a black King to check it, if there is a white pawn protecting the white King, preventing the black King from taking the white King?
7
votes
2answers
1k views

FIDE rules when opponent accidentally promotes to your Queen

This happened to someone else recently in a time scramble during an OTB game. His opponent promoted a pawn and placed a Queen of the wrong color on the board. He was corrected by the player and the ...
7
votes
4answers
1k views

Outcome of a game in case of an illegal checkmate

Suppose that, in an amateur rapid play tournament (where supervision is inappropriate), the following position appears: [fen "5K2/8/1q6/1N1k4/8/8/8/2R1R3 w - - 1 1"] 1. Re5+? Qc5+? {illegal} 2. Rxc5#...
6
votes
1answer
440 views

We found out that we made an illegal move later on in the game [duplicate]

I am playing with my friend. I didn't notice that my king was in check, so I made an illegal move. We noticed this after several more moves. What should happen next? Do we restart the game or ...
6
votes
2answers
1k 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. ...
6
votes
1answer
960 views

Can a win be claimed on the second illegal move if the first wasn't raised?

First of all, I don't think this is a duplicate of what happens on the first illegal move in a game. This is what happens after the second if the first is unclaimed. The setting is a tournament under ...
6
votes
2answers
450 views

How to create PGN notation with wrong moves in it?

I was as chess trainer with some young guys on a tournament, and wrote down some of their games. In nearly every game, there were wrong moves in it: king is in check, but does not move or react; ...
5
votes
2answers
481 views

Can I move a piece protecting the king if it keeps protecting on its new location?

Situation: there's a piece between the king and an opponent’s piece. If this piece were not there, it would be a check. If I were to try and move the protecting piece somewhere and leave the king ...
5
votes
1answer
228 views

Why isn't the active color allowed to be in check in a FEN legal position?

The title says it. Reading up on how to describe the position of a board, all of the requirements make sense (like two kings not being on adjacent squares and so on) except for the active color being ...
5
votes
1answer
514 views

Can you claim an illegal move in Blitz after pressing your clock (but without making a move)?

In Blitz under FIDE rules, Player A makes and completes an illegal move by pressing the clock. Player B states that Player A's move is illegal, does not make a move, but quickly presses his own clock, ...
5
votes
2answers
190 views

Is this move valid in the rollerball chess variant?

Can the white King move a space to the right, into the original location of the black king? This would be disallowed in standard chess, as one cannot intentionally put themselves into check. However, ...
4
votes
3answers
18k views

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?
4
votes
1answer
221 views

Touch move and capture sequence

When considering the touch move rule, I am still unclear about the legal sequence for a capture. Example, white intends to capture a took on a8 with rook on a1 (open file). Does white have to touch ...
4
votes
1answer
127 views

How can I use pgn-extract to remove a game from a pgn file when there is an illegal move?

How can I use pgn-extract to remove a game from a pgn file when there is an illegal move?
3
votes
1answer
1k views

Illegal move or checkmate? [duplicate]

I was playing chess with an opponent. He had his queen in front of his king. I attacked the queen and he moved her, exposing his king directly to my rook. It was my turn to move, not his. We couldn't ...
3
votes
1answer
97 views

How to detect invalid pawn structures (not based on opponent material) for FEN valdation?

I'm going to further expand a FEN validation function I have been working on for some time to include illegal pawn formations such that: ... for example white pawns could never be on a2, a3, and ...
3
votes
2answers
291 views

Illegal move or forfeit on time - who wins this 5-minute match?

In a 5-minute match a player makes an illegal move leaving his king in a check position. This usually gives the victory to the opponent, if he sees it and captures the king. Otherwise, if the opponent ...
2
votes
3answers
369 views

How to notify check when a player leaves himself in check

I'm learning to play chess. Twice we had a situation where the white player moved a piece that was blocking the black Queen from checking the white King. There was no move available to announce "...
2
votes
1answer
294 views

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 ...
2
votes
1answer
236 views

Are there any legal positions known to be impossible to come to in a normal game? [duplicate]

There are some fairly obvious ways to set up a chess board that cannot possibly happen: both kings simultaneously in check would be one. There are some positions that seem impossible in a normal ...
1
vote
3answers
473 views

What happens if I push a pawn to the 8th rank and press the clock before promoting? [duplicate]

What happens if I push a pawn to the 8th rank and press the clock before converting it to another piece? Does it make a difference if it's Blitz or not?
1
vote
4answers
486 views

Blitz Touch Move Rule

In a "friendly" blitz game I got into an argument with my opponent in the following scenario: My opponent's knight was pinned to his king. He did not notice and touched his knight to move it. I ...
1
vote
1answer
147 views

How is this move illegal?

I'm black and it's my turn. I'm playing in the Arena chess player against Stockfish. This is my current board: [fen ""] [startply "31"] 1. e4 d5 2. exd5 e6 3. dxe6 fxe6 4. Nf3 Nf6 5. Bc4 c6 6. O-O ...
1
vote
2answers
197 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 ...
1
vote
2answers
113 views

Way to Logically Predict Approximate Chess Rating in Pop-Culture Games [closed]

After seeing a video of an analysis on the chess game in A Game of Shadows between Sherlock Holmes and Moriarty, it made me wonder what their fictional ratings would be around. Other games like the ...
1
vote
4answers
503 views

Is it possible to play 1 minute bullet with no increment over the board?

Playing 1 minute bullet games with no increment on the Internet is hard enough, but what about over the board, in real life with an actual wooden board? Would it be possible, or would 90% of the ...
0
votes
1answer
250 views

Rook and knight used together within the same move - legal?

This is my first question on chess beta and I don't know if I'm insane or if the cpu is broken. So I was playing chess against a CPU on the iPhone with the app 3D Chess Game, and the CPU (playing ...
-2
votes
2answers
202 views

What happens if I realize that I made an illegal move? [closed]

Say I somehow make an illegal move, what happens? If I realize, can I then take it back, and make it legal? If so, how?
-2
votes
1answer
92 views

Checking on the legality of a move [duplicate]

I moved my white King to d4, taking black's bishop. This put the king in a checkmate with black's knight on c6. Is this move legal or illegal? Thank you.