Check is a condition in chess where a King is under direct attack by one or more enemy pieces. Because the King is the most vital piece on the board and can never be captured, putting the King in check is a direct threat to end the game.
When your King is in check, the rules of chess dictate that you must resolve the check immediately on your very next turn. Making any move that leaves your King in check is strictly illegal.
How to Escape Check: The CPR Method
Whenever your King comes under attack, remember the CPR acronym to find all legal ways out:
C — Capture the attacking enemy piece.
P — Protect (block) by placing a piece between your King and the attacker.
R — Run by moving your King to a safe, unattacked square.1. Capture (C)
If one of your pieces (or even the King itself, provided the attacker is undefended) can capture the checking piece, the threat is eliminated immediately.
2. Protect / Block (P)
If the check is coming along a line from a Queen, Rook, or Bishop, you can slide a defending piece into the path between the attacker and your King.
Note: You cannot block a check from a Knight or Pawn, because Knights leap over intervening squares and Pawns attack from an adjacent square.
3. Run (R)
Move the King to any of the 8 adjacent squares, provided that destination square is not attacked by an enemy piece.
Double Check: The Deadliest Attack
A Double Check occurs when two pieces check the King at the same time—typically when one piece moves to give check while opening a line for a second piece behind it (a discovered check).
In a double check, capturing one attacker still leaves the other, and blocking one ray does not block the other. Therefore, the King MUST run.
For experienced players
In algebraic chess notation, a standard check is written with a plus sign (e.g., Bxf7+), and a double check is frequently written with a double plus (++).
See also:Checkmate·Stalemate·Double check·Discovered attack