Illegal move in chess: what counts and the penalty

Two of the moves on this list break no rule about how a piece travels. You can play an illegal move without moving a piece to a wrong square at all.

An illegal move is any move the Laws of Chess do not allow. These are the ones that actually happen in games:

• Moving a piece so that your own king is left under attack.
• Leaving your king under attack when it was already in check.
• Moving your king onto a square an enemy piece attacks.
• Moving your king next to the enemy king.
• Capturing a defended piece with your king.
• Moving a piece in a way that piece cannot move, such as a rook along a slant.
• Castling when the rules do not allow it, for example out of check or through an attacked square.
• Capturing en passant a move too late.
• Leaving a pawn on the last row without changing it into another piece.

Two more count as illegal moves under article 7.5, even though no piece went to a wrong square. Pressing your clock without having moved is one. Using two hands to make a single move is the other.

Because of the pin. A pin happens when one of your pieces stands between an enemy attacker and your own king.

While it stands there, that piece cannot move at all. Every square it could go to would leave your king under attack, and that is illegal.

This is where nearly every illegal move at club level comes from. The player sees a knight, sees a good square, and forgets the bishop on the far side of the board.

The fix is a habit. Before you touch anything, follow every line that points at your king. That means the row it stands on, the column it stands on, and the two diagonals through it. A diagonal is a slanting line of squares that all share one colour. Ask which of your own pieces is standing on one of those lines.

Your king may not move to a square an enemy piece attacks. That includes capturing a piece that is guarded.

It also includes standing next to the enemy king. The two kings must always keep at least one empty square between them.

When you are in check you have exactly three ways out. Move the king to a safe square. Put a piece in the way. Or capture the piece that is giving check. If none of those is possible, the game is over.

There is one case with no way out at all. When two enemy pieces give check at the same time, called a double check, blocking and capturing are both useless. Only a king move can be legal.

Article 7.5 of the FIDE Laws sets it out in two steps.

First the board is put right. The illegal move is taken back and the pieces go back where they were before it. If the player has touched a piece, the touch-move rule still applies to whatever they play instead.

Then the penalty. In a standard-length game:

1. The first completed illegal move gives your opponent two extra minutes on their clock.
2. The second illegal move in the same game loses the game.

There is one exception to the second rule. If your opponent could not possibly checkmate you with the pieces they have left, the game is a draw instead of a loss.

A move only counts once it is completed. In practice that means you let go of the piece and pressed your clock.

Since 2018 rapid and blitz follow the same two steps as long games. The first illegal move gives your opponent extra time and the second one loses.

There is a practical difference. In a long game an arbiter watches and steps in. In blitz nobody is watching your board, so your opponent has to notice and claim it. Once you have both played on, it is usually too late.

Some events publish their own rules for fast play. Read the tournament regulations before the first round, not after your first argument.

No, the penalty is the same, but pawns produce their own set of mistakes.

• A pawn moves straight forward and captures diagonally. It can never capture the piece directly in front of it.
• A pawn may move two squares only from its starting row, and only if both squares are empty.
• A pawn can never move backwards.
• En passant is legal on the very next move and never again.
• A pawn that reaches the last row must be changed at once. Leaving it as a pawn is an illegal move, and article 7.5.2 says the piece is replaced with a queen.

Our live play follows the tournament rules instead of stopping you.

When you pick up a piece, no dots appear to show you where it may go. You may drop it on a square that is not allowed.

If you do, the move is taken back and your opponent is given extra time. That is fifteen seconds in bullet, one minute in blitz and rapid, and two minutes in a classical game.

Make a second illegal move in the same game and you lose it, exactly as article 7.5 says.

There are no premoves, and your clock keeps running if your connection drops. It is the closest thing to sitting at a real board.