In chess, a skewer (or X-ray attack) is an attack upon two pieces in a line and is similar to a pin. A skewer is sometimes described as a "reverse pin"; the difference is that in a skewer, the more valuable piece is in front of the piece of lesser value. The opponent is compelled to move the more valuable piece to avoid its capture, thereby exposing the less valuable piece which can then be captured (see chess piece relative value). The long-range pieces (queen, rook, and bishop) can skewer.
|This article uses algebraic notation to describe chess moves.|
Skewers can be broken down into two types: absolute and relative. In an absolute skewer, the king is in check, therefore the check must be handled (under the rules of chess), whereas in a relative skewer, the pieces involved don't necessarily need to be addressed.
In this diagram, with Black to move, the black queen is skewered by White's bishop. To avoid capture of the queen, Black must move the queen, and on the next move, White can capture the rook. This is a relative skewer; Black is likely to move the queen, which is more valuable than the rook—but the choice is still available.
In this diagram, with White to move, the white king is skewered by the black bishop. This is an absolute skewer, because the rules of chess compel White to get out of check (if possible). After White chooses one of the handful of legal moves available, Black will capture the white queen.
Because the skewer is a direct attack upon the more valuable piece, it is generally a much more powerful and effective tactic than the pin. The victim of a skewer often cannot avoid losing material (though it may be possible if, for example, either piece can give check, thereby forcing the skewering side to move out of check instead of being able to capture either piece, or if it is possible to move a less valuable piece in the way); the only question is which material will be lost. The skewer occurs less often than the pin in actual play. When it does occur, however, it is often decisive.
Example from game
In this 1989 game between Nigel Short and Rafael Vaganian, White sacrifices a bishop to win a queen by a skewer. White has just moved 51. Be5+. If Black moves 51...Kxe5 to avoid the immediate loss of the queen, 52.Qc3+ wins the queen by a skewer. Black resigned in this position (Hooper & Whyld 1992:374).
If there is empty space between the skewering and the skewered pieces, it may be possible to convert the skewer into a pin by moving a lower-valued piece to intervene.
- Reinfeld, Fred (1955). 1001 Winning Chess Sacrifices and Combinations. Wilshire Book Company. p. 151. ISBN 0-87980-111-5. Check date values in:
- Short vs Vaganian
- Hooper, David; Whyld, Kenneth (1992), "skewer", The Oxford Companion to Chess (2nd ed.), Oxford University Press, ISBN 0-19-280049-3
- Chess Tactics Repository - Skewers - Collection of chess problems involving skewers
- Edward Winter's "The Chess Skewer" (Chess Notes Feature Article)