Special moves and rules

Castling moves the king two squares toward a rook and jumps that rook to the square the king crossed, in a single move. It is legal only if neither piece has moved, nothing stands between them, and the king is not in check, does not pass through an attacked square, and does not land in check.

En passant lets a pawn capture an enemy pawn that has just moved two squares forward and landed beside it. The capturing pawn moves diagonally to the square the enemy pawn skipped, and the right lasts for that one move only.

A pawn that reaches the far rank must immediately be replaced by a queen, rook, bishop or knight of the same colour, chosen by its owner. Choosing anything other than a queen is called underpromotion.

A king is in check when an enemy piece attacks it, and the player in check must get out of it at once. If there is no legal way to do so, it is checkmate and the game is over.

Stalemate happens when the player to move has no legal move and is not in check. The game ends immediately in a draw, even if one side has far more material.

A player may claim a draw when the same position occurs for the third time with the same player to move and the same castling and en passant rights. Under FIDE rules a fivefold repetition ends the game automatically.

A player may claim a draw if each side has made fifty consecutive moves without any capture or pawn move. Under FIDE rules seventy-five such moves end the game automatically.

The game is drawn when neither player can possibly checkmate by any legal sequence of moves, such as king against king, king and bishop against king, or king and knight against king.