Vacating sacrifice

A vacating sacrifice deliberately gives up a piece in order to empty the square it occupies. The intended gain is not found in the offered piece, but in allowing another piece of the same side to use that square. After the sacrifice, a queen, rook, bishop, knight, king, or pawn can occupy the cleared point and carry out a threat that was previously impossible.

The sacrifice must preserve the tempo, meaning the opportunity to play the continuation before the opponent can defend. The piece therefore often leaves with check, a direct attack on the king, a capture, or another threat. Sometimes the opponent must capture it; in other cases it is enough that the piece cannot be saved, because the main threat is already more urgent.

This is a special form of square clearance. In ordinary clearance, the piece may move away without being lost. Here giving up the piece is an essential part of the method. If its departure also opens a file, rank, or diagonal, the move combines this idea with line clearance. The return must be concrete: a final attack on the king with no legal defense, a pawn reaching the last rank and becoming another piece, a larger gain of pieces, or a lasting advantage that clearly justifies the offer.