Cross-check

A cross-check occurs when the checked player makes one move that gets out of check and checks the opponent at the same time. The move does more than satisfy a legal obligation: it immediately changes which player must respond.

The most common form interposes a piece between the attacker and the king, so the piece blocks the original check while attacking the opposing king. Another form moves a piece or the king and reveals a discovered check, meaning that the move opens the line of another piece that had been hidden behind it.

Why it is so forcing

A check must be answered. A cross-check can therefore seize the initiative, the ability to keep the opponent responding to threats, and function as an unusually strong counterthreat. It matters in tactical positions and some queen endings, where a chain of checks can decide whether a king escapes, moves repeat, or a pawn advances.

Not every check made after receiving one is normally given this name. When the checking piece is simply captured and the capture happens to give check, many descriptions reserve cross-check for a block or discovered-check mechanism. The essential feature is that the reply removes one check and gives another on the same move; in stricter usage, this occurs through a block or a discovered check.