Check Explained
What is check, and how to respond to check.
Check
In chess, a check occurs when a player's king is under direct threat of capture by one or more of the opponent's pieces. When the King in danger then an immediate response is required - the player whose king is in check must make a move that removes the threat of capture.
The white King is in check - attacked by the black Rook at E8- and can only move out of the line of attack.
Responding to Check
Move the King
The king can move to a square where it is not in check. This square must not be under attack by any of the opponent's pieces.
Block the Check
Another piece can be moved to a position between the king and the attacking piece, thereby blocking the check. This is only possible if the checking piece is not a knight, as knights can jump over pieces.
Capture the Attacking Piece
The piece that is delivering the check can be captured, either by the king itself or by another piece.
Rules
Mandatory Response
When in check, the player must make a move that eliminates the check. No other move is permitted.
Cannot Castle
If the king is in check, castling is not allowed.
Checkmate
If the player whose king is in check has no legal move to remove the check, it is a checkmate, and the game ends with a win for the player delivering the checkmate.
Understanding check is fundamental to playing chess effectively, as the ultimate goal is to deliver checkmate, a position where the opponent's king is in check and there are no legal moves to escape.