Relative pin

A relative pin occurs when a piece blocks a line attack against something important other than its king. Moving the piece is legal, but it exposes a queen, rook, mating threat, or another target whose cost is usually greater.

Unlike an absolute pin, the rules do not immobilize the piece. The restriction is practical: the player decides whether the consequence of moving is acceptable. Breaking the pin can sometimes be best because it creates checkmate, wins more material, launches a counterattack, or leads to a favorable exchange.

The position cannot be judged only by nominal piece values. Calculate what happens if the pinned piece moves and what happens if it stays. The exposed queen may be defended, the attacker may become trapped, or the pinned piece may have a more urgent threat.

The defender may also remove the pin before making that choice by moving the rear target, attacking the pinning piece, interposing another piece, or creating a threat with tempo. The term describes the geometry and does not guarantee a gain.