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Ponderchess / Glossary

Pin in chess

A pin is an attack on a piece that cannot move without exposing a more valuable piece behind it. If the piece behind is the king, the pin is absolute and the pinned piece may not legally leave the line; otherwise it is relative and moving it usually loses material.

White to move. The bishop on b5 pins the knight on c6 to the king on e8, so the knight has no legal moves. d5 attacks it a second time with a pawn. Whatever Black plays, dxc6 follows, and White wins the knight for a pawn.1.d5

How a pin works

Only line pieces can pin: bishops along diagonals, rooks along ranks and files, and queens along both. The pinned piece stands in front, and the more valuable piece stands behind it on the same line.

Familiar examples come straight from the opening. A bishop on b5 pins a knight on c6 to a king on e8, and a bishop on g5 pins a knight on f6 to a queen on d8. The first is absolute; the second is relative, because moving the knight is legal but gives up the queen.

Why pinned pieces are weak

A pinned piece is half paralysed. It cannot run away when attacked, and its defence of other pieces is often an illusion, because it cannot leave the line to recapture. The standard way to exploit a pin is to attack the pinned piece again, ideally with a pawn, since a pawn is the cheapest attacker.

A pinned piece is not powerless, though. An absolutely pinned piece still stops the enemy king from stepping onto the squares it attacks, and a relatively pinned piece can still move if doing so creates a bigger threat. Légal's mate is the classic case of a pinned knight moving anyway and giving up the queen for checkmate.

Breaking a pin

There are four usual remedies: move the piece behind off the line, put a protected piece in between, attack the pinning piece (as with ...a6 against a bishop on b5, or ...h6 against a bishop on g5), or create a counter-threat. Breaking a pin with pawn moves such as ...h6 and ...g5 can weaken your own king, so check what it costs first.

Common mistakes

  • Moving a relatively pinned piece and losing the queen or rook behind it.
  • Counting a pinned piece as a defender when it cannot legally leave the line.
  • Leaving the king and queen on the same open file or diagonal as an enemy bishop, rook or queen.

Questions about pin

What is the difference between an absolute and a relative pin?

In an absolute pin the piece behind is the king, so the pinned piece cannot legally move off the line. In a relative pin the piece behind is something else, so moving is legal but usually costs material.

What is the difference between a pin and a skewer?

In a pin the more valuable piece is behind. In a skewer the more valuable piece is in front, and it must move and expose the piece behind it.

Can a knight pin a piece?

No. A knight jumps rather than moving along a line, so only bishops, rooks and queens can pin.

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