26 April 2012

Glossary of Tactics: Pins

In chess, a pin is an attack of two targets along a rank, file, or diagonal such that moving one attacked piece renders the other vulnerable to capture. When a piece is pinned against the king, it is an absolute pin: the pinned piece cannot legally move. In a relative pin, the pinned piece may legally move, but often with dire consequences.

In this position from a blindfold exhibition by Miguel Najdorf, Black's knight on c6 cannot legally move.

White to move
Najdorf played 10.d5, a technique known as piling on: attack a pinned piece with another piece, and sometimes the defense will crumble. The game continued 10...a6 11.Bxc6+ Bxc6 12.dxc6 and Najdorf has won two pieces for one.

In contrast, Black's relative pin of the knight against the queen in this famous game played in Paris in 1851 is ineffective. The knight is able to move, winning a pawn.

White to move
White played 5.Nxe5. After 5...dxe5 6.Qxg4, we see that White gained a pawn, while exchanging knight for bishop. A pin by a bishop was transformed into a discovered attack against that bishop. However, in the actual game, Black preserved his bishop by capturing White's queen. Alas, the cost was the Black monarch.

5...Bxd1 6.Bxf7+ Ke7 7.Nd5#.

Bishops, rooks, and queens are the only chess pieces capable of pinning one piece to another. Likewise, these three pieces are capable of a skewer, a sort of pin in reverse, and are essential pieces in the construction of threats of discovered attacks.

A pin may also be executed against a piece and a critical square. In the position below from Anderssen -- Staunton, London 1851, Black's pawn on h6 is pinned, although it has no way to move off the h-file at the moment. Staunton just played 21...h6 to avoid checkmate.

White to move
3r1rk1/b4pp1/p3p1np/1pp1P2Q/5PP1/3BB2R/qPP4P/5R1K w - - 0 22

Anderssen offers the pawn an opportunity to vacate the h-file, and piles on pressure along the same. If Black plays 22...hxg5, then White wins instantly: 23.Qh7#. Anderssen's exemplary attack employed pins and other tactics to break down Black's defenses. Staunton proved resourceful in defense, but errors made earlier in the game were decisive and his position proved indefensible.

22...Rxd3 23.cxd3 Qd5+ 24.Rff3 Ne7 25.gxh6 g6 26.h7+ Kh8 27.Qg5 Nf5 28.Qf6+ Ng7

White to move

The knight is pinned, and if White can simply pile on with the dark-squared bishop, the game will be over.

29.f5! Qb3 30.Bh6 Qd1+ 31.Kg2 Qe2+ 32.Rf2 Qg4+ 33.Rg3 Qxg3+ 34.hxg3 Rg8 35.hxg8Q+ Kxg8 36.Qxg7# 1–0

So, we see that pins were useful to the winner of the first International Chess Tournament.

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