X-Ray Attack
An x-ray attack is influence that's real but temporarily hidden — a piece attacking down a rank, file, or diagonal that's currently blocked by another piece, friendly or enemy, so that the attack only becomes visible once that piece is removed. Unlike a discovered attack, nobody has to move the blocking piece on purpose; a trade sequence removes it just as effectively, and the attacker was there the whole time even though the position didn't look like it.
Why 'currently blocked' doesn't mean 'not a threat'
The single most useful thing to take from this tactic is a correction to how you evaluate a defended piece: a square isn't safe just because you can currently count enough of your own defenders against the visible attackers. If an enemy piece sits behind another piece on the same line — including behind one of ITS OWN pieces — that piece is still a real attacker on anything further down the line, and it will become active the moment the pieces in front of it get traded away, whether or not either side intended that.
Starting position. A rook hidden behind its own knight on an open file (illustrative position, not from a recorded game).
A rook that looks irrelevant behind its own knight turns out to have been the real attacker on the square the whole time.
The exchange-sequence trap
This is where x-ray attacks actually cost people games: a capture on a contested square looks even because both sides seem to have one attacker and one defender, and only after the pieces start coming off does it become clear that one side had a second attacker hiding behind the first the entire time. In the position above, Black's rook looks like a safe recapture right up until it discovers that White's rook was never really blocked — it was simply waiting one piece back.
Counting correctly before you trade
Before initiating or accepting a trade on a contested square, trace every rank, file, and diagonal through that square outward in both directions, past the first piece you find, and keep going until you hit an empty square or the edge of the board. Any piece you find beyond the first blocker — yours or the opponent's — is a real participant in the coming exchange, not a spectator, and needs to be counted alongside the attackers and defenders that are immediately visible.
Using it on purpose, not just defending against it
Once you're deliberately looking for it, x-ray influence is something you can set up rather than just stumble into: placing a rook or queen behind your own minor piece on a file the opponent is likely to contest is a way of quietly adding an attacker to a square without it being obvious yet. The piece in front doesn't even need a specific plan — it just needs to be willing to trade eventually, at which point the hidden piece behind it takes over.
Doubling two pieces of your own on purpose, both aimed at the same target, is a related but distinct idea called a battery — the difference is that a battery is deliberate and visible from the start, while an x-ray attack is exactly the kind of influence that's easy to miss because it's sitting behind someone else's piece rather than your own.
Frequently Asked Questions
Does an x-ray attack require the blocking piece to be an enemy piece?
No — it works the same whether the piece in front belongs to you or the opponent. What matters is only that a piece is standing on the line between your attacker and the target square, and that it's realistically going to move or be captured at some point in the sequence being calculated.
How is this different from a pin?
A pin needs exactly two enemy pieces on the same line, with the front one restricted because moving it would expose the back one. An x-ray attack doesn't require the blocking piece to be restricted at all — it can move freely, and the whole point is about what your own piece is secretly influencing through it, not about limiting the blocker's options.
Why do club players miss x-ray attacks more than titled players?
Mostly because evaluating a square as 'defended' is usually done by counting only the pieces immediately visible as attackers and defenders, and stopping there — tracing every line all the way through the first piece to whatever sits behind it takes an extra, deliberate step that's easy to skip when a position looks calm.