Chess tactics
What Is an X-ray Attack in Chess?
An X-ray is the effect of a bishop, rook, or queen through another piece on the same line. The piece behind still attacks or defends the squares beyond, because as soon as the piece in front moves or is captured, its line opens.
Example
1. Qxe8+ Qf8
The rook on e1 looks through the black queen at e8. That is why Qxe8+ works: if Black recaptures with Qxe8, the queen leaves the file and Rxe8 is mate. Black has to play Qf8 instead and is simply a rook down.
X-ray attack and X-ray defense
In an X-ray attack, a piece hits a target through an enemy piece. The skewer is the best-known case: the front piece moves and the one behind is captured. In an X-ray defense, a piece guards a square through an enemy piece, so it counts as a defender in a trade even though something stands in the way.
The example is an X-ray defense of e8. On the surface the black rook is defended by the queen and attacked only by the white queen. But the white rook on e1 also guards e8 through the black queen, so the recapture would open the file for mate.
Counting exchanges with X-rays
When you count attackers and defenders on a square, include pieces lined up behind other pieces on the same line. Doubled rooks, and a queen behind a rook, add their power to the front piece once it captures. Missing an X-ray is a common reason a trade goes wrong.
How to spot one
Trace each of your long-range pieces along its lines, past the first piece it meets. If an important square or the enemy king is behind that piece, ask what happens when the piece in the middle moves or is exchanged.
Common questions
Is an X-ray the same as a skewer?
A skewer is one kind of X-ray attack. X-ray is the wider term and also covers defending or controlling a square through another piece.
Which pieces can make an X-ray?
Only bishops, rooks, and queens, because the effect works along ranks, files, and diagonals. Knights, kings, and pawns do not act along lines.
Why is it called an X-ray?
Because the piece behaves as if it can see through the piece in front of it, the way an X-ray sees through an object. Its power is only hidden, not blocked for good.
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