Interference (chess)

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This article uses algebraic notation to describe chess moves.

Interference occurs when the line between an attacked piece and its defender is interrupted by sacrificially interposing a piece. It is a chess tactic which seldom arises, and is therefore often overlooked. Opportunities for interference are rare because the defended object must be more valuable than the sacrificed piece, and the interposition must itself represent a threat.

Image:chess zhor 26.png
Image:chess zver 26.png a8 b8 c8 kd d8 rd e8 f8 bd g8 h8 Image:chess zver 26.png
a7 pd b7 pd c7 pd d7 e7 f7 g7 h7 pd
a6 b6 c6 d6 e6 f6 g6 pd h6
a5 b5 c5 d5 e5 pl f5 nl g5 h5
a4 b4 c4 d4 e4 f4 g4 h4
a3 b3 c3 d3 e3 f3 g3 h3 pl
a2 pl b2 c2 d2 qd e2 ql f2 pl g2 pl h2
a1 b1 c1 d1 e1 rl f1 g1 kl h1
Image:chess zhor 26.png

In the position at left, White to play will apparently be obliged to retreat the knight from f5, because the squares to which it could advance are all guarded. However, the interference move 1.Nd6+ interrupts the black rook's defense of the black queen. If Black plays either 1...cxd6 or 1...Bxd6, White will capture Black's queen. Therefore Black has no better play than 1...Rxd6 2.exd6 Qxe2 3. Rxe2 Bxd6, conceding the exchange for a pawn.

A more subtle example of interference occurs when the interposing piece interrupts two lines simultaneously. In this case, the moving piece does not have to pose a threat by itself. Instead, it makes the opponent trip over his own feet, so to speak, because capturing the offending piece will necessarily break one line of defense or the other.

Image:chess zhor 26.png
Image:chess zver 26.png a8 b8 rl c8 d8 rd e8 f8 g8 h8 Image:chess zver 26.png
a7 pl b7 c7 d7 e7 f7 pd g7 h7 kd
a6 b6 c6 d6 e6 f6 g6 pd h6 pd
a5 b5 c5 d5 e5 f5 nd g5 h5
a4 b4 nl c4 d4 e4 bd f4 g4 h4
a3 kl b3 pl c3 d3 e3 f3 g3 h3
a2 b2 bl c2 pl d2 rd e2 f2 g2 h2 pl
a1 b1 c1 d1 e1 f1 g1 h1
Image:chess zhor 26.png

In the position at right, White is at a material disadvantage, and apparently can't queen the a-pawn because the black bishop guards the queening square. However, 1.Nd5 interferes with the bishop and with the black rooks' defense of each other. If 1...Bxd5, 2.Rxd8 is crushing. The best Black can do is 1...R2xd5, interfering with the bishop's guard of a8 and allowing 2.a8Q.

Although interferences are quite rare in actual play, they are a common theme in chess problems. The device in the last example above, in which a sacrifice occurs on the intersection of the defensive lines of two differently moving pieces, is known to problemists as a Novotny. Various other types of interference are given specific names in problem terminology, including the Grimshaw, Plachutta where the two pieces both move orthogonally (see a beautiful example by Tarrasch), Anti-Bristol, Holzhausen and Wurzburg-Plachutta.

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