Chess tactics
Pin
A pin freezes a piece in place because moving it would expose something more valuable behind it.
What it is
A pin is a line attack — bishop, rook or queen — through one enemy piece onto a more valuable one behind it. If the king is behind, the pinned piece legally cannot move at all (an absolute pin). If a queen or rook is behind, moving is legal but loses material (a relative pin). A pinned piece is a defender that has stopped defending, which is why the follow-up is usually to attack it again with something cheap.
How to spot one
- Enemy king and another piece on the same rank, file or diagonal with exactly one piece between them.
- A knight defending a mate square while standing in front of its own queen.
- Your bishop and their king already aligned, with a piece stepping onto that diagonal.
- After you pin, look for a pawn that can hit the pinned piece. It cannot run.
A worked example
The bishop on b4 pins the knight on e2 against the king on e1: the knight is frozen because moving it would leave the king in check. White has to break the pin or defend the knight again, because Black can simply add another attacker.