What check is
Check is an attack on the king. If an enemy piece attacks your king, you must remove the threat at once. Leaving the king in check, or moving it into an attacked square, is illegal.
You do not have to say “check” out loud — that is just a habit from casual games.
Three ways to defend
There are only three ways to answer a check:
- Move the king to a safe square.
- Block — put one of your pieces between the king and the attacking piece.
- Capture the piece giving check.
In this position White has all three options:
- move the king: Kd1, Kd2 or Kf1;
- block with the bishop: Be2;
- capture the rook: Rxe8+.
The best move is the capture. The white rook takes on e8 and itself gives check to the black king. And since the king is hemmed in by its own pawns, it is also checkmate!
1.
Double check
Sometimes two pieces give check at once: one moves and opens a line for the other. A double check cannot be blocked, and you cannot capture both pieces at once — the only option is to move the king. That makes double check one of the most powerful tactical weapons.
Check and checkmate
If none of the three defences works, it is checkmate and the game is over. If there is no check but no legal move either, it is stalemate, and the game ends in a draw.
A chess player's most important habit: before every move, check whether the opponent has any checks, captures or threats. This simple check saves you from most defeats.