Discovered check
A discovered check is a check from a piece that did not move: a bishop, rook or queen is unmasked when the piece in front of it leaves the line to the king.
Here the check comes from the piece behind. Your own piece blocks a line between a bishop, rook or queen and the enemy king; when it moves, the line opens and the king is suddenly in check. The piece that moved has not been answered yet, because the opponent must deal with the check first.
That gives the mover a free hand. It can capture a queen, fork two pieces, or even give a second check of its own, which turns the whole thing into a double check. Since a block or capture of the checking piece is often unavailable, the usual reply is a king move, and then the mover's threat goes through.
A good discovered check is also a threat you can build before moving anything. A bishop on a diagonal aimed through your own knight at the enemy king makes that knight a loaded spring; any time it lands on a square that attacks something big, it wins material.
When defending, look for lines where your king sits behind an enemy piece and a rook, bishop or queen of theirs stands further back. Moving the king off the line, or breaking up the alignment, takes the sting out.
In the diagram White plays Nc6+. The knight leaves the e-file, so the rook on e1 checks the king on e8, and the knight itself now eyes the queen on d8. If Black blocks with Qe7, Nxe7 wins the queen outright because the rook protects the knight, and any king move loses the queen as well.
Compare it with Royal fork. A royal fork is a fork that attacks the enemy king and queen at the same time, most often with a knight, so the king must move and the queen is lost.
A neighboring idea is Windmill. A windmill is a repeating pattern in which a rook moves away to give a discovered check, captures a piece, returns with check, and repeats, winning another enemy piece with each swing.
Also worth reading is Zwischenzug. A zwischenzug, German for in-between move, interrupts a sequence both sides expect: instead of recapturing or answering a threat at once, a player slips in a check or bigger threat first.
Knowing "Discovered check" helps most once you can spot it in a real game. A first lesson with George Li starts from your own games and finds the tactics you keep missing.
Related terms
In a discovered attack one of your pieces steps off a line, and that move unmasks a bishop, rook or queen standing behind it, so a single turn produces two threats.
A double check is a single move that puts the enemy king under attack from two pieces simultaneously, typically one that moved and one it unmasked, so only a king move can answer it.
A double attack is one move that creates two threats at once, whether they come from a single piece or from two, and whether they aim at pieces or at checkmate.
A royal fork is a fork that attacks the enemy king and queen at the same time, most often with a knight, so the king must move and the queen is lost.
Guides that go further
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