Learn · Tactics
Discovered Attacks and Double Check
How discovered attacks, discovered checks and double checks work, why they are so powerful, and how to set them up and defend against them.
A discovered attack happens when one piece moves out of the way and reveals an attack by another piece standing behind it. It's one of the most powerful tactics in chess because it creates two threats with one move: whatever the moving piece does, plus the attack it uncovers.
How it works
You need two pieces on the same line: a long-range piece behind (a bishop, rook or queen) and a front piece blocking it. When the front piece moves, the line opens.
Imagine a white rook on e1, a white knight on e4 and a black queen on e8. The knight blocks the rook's file. If the knight jumps to f5, attacking a black rook on d6, Black faces two threats: the knight's, and the rook's attack on the queen. Black usually can't answer both.
Discovered check
A discovered check is a discovered attack where the uncovered piece gives check. It's even stronger, because your opponent must deal with the check first, and the piece that moved is free to do almost anything: capture the queen, grab a rook, or go anywhere it likes, even to a square where it can be taken, since the check must be answered first.
Think of a rook on the same file as the enemy king with your own bishop in between. Every time the bishop moves, it gives check. The bishop can take something on each move while the rook keeps checking: this repeating pattern is called a windmill, and it can strip an entire position of its pieces.
Double check
A double check happens when the moving piece gives check too, so the king is attacked by two pieces at once. This is the most forcing move in chess. You can't block two checks with one piece, and you can't capture two checkers with one move, so the king must move. If it has no safe square, it's checkmate, even if every other piece of the defender is ready to help.
A well-known trap in the Petrov Defence shows how forcing moves overwhelm a defender. After 1.e4 e5 2.Nf3 Nf6 3.Nxe5 Nc6 4.Nxc6 dxc6 5.d3 Bc5 6.Bg5?? Nxe4! 7.Bxd8?? Bxf2+ 8.Ke2 Bg4#, Black gives up the queen and mates with two bishops and a knight. It isn't a double check, but it shows the same principle that makes discovered attacks so dangerous: when the king is forced to respond, the defender has no time to save the rest.
A cleaner example of double check: a white rook on e1 and a black king on e8, with a white knight on e4 between them. If the knight jumps to d6 or f6, it gives check, and so does the rook down the newly opened e-file. Two checks at once: the king must move, and next turn the knight is free to take whatever it attacks.
Setting one up
- Line up your long-range piece with a target. Put a rook on the same file as the enemy king or queen, or a bishop on the same diagonal, even when your own piece is in the way.
- Make the front piece useful. The piece that moves should have a strong move available: a capture, a check, or an attack on something valuable.
- Look at the king's file and diagonals. Castled kings on g1 or g8 often sit on the same diagonal as a bishop (a7-g1 or a2-g8). If one of your pieces is blocking that diagonal, ask what happens if it moves with tempo.
Defending against them
Discovered attacks are hard to defend once they're on the board, so the trick is to avoid the setup:
- Don't leave your king and queen on lines that enemy bishops, rooks or queens control, even if a piece is currently in the way. "In the way" is temporary.
- Watch enemy pieces that block their own long-range pieces. If your opponent has a knight in front of a rook aimed at your queen, that knight is a loaded gun. Move the target or challenge the rook.
- When in doubt, step off the line. Moving your king one square, from g8 to h8 for example, often removes the whole danger.
Discovered attacks in the opening
They show up early more often than you'd expect. A common pattern in 1.e4 e5 openings: after the e-file opens, a knight on e5 or e4 stands in front of a rook or queen on the e-file, with the enemy king still uncastled on e8 or e1. Any knight move can then reveal a check. This is one more reason to castle early.
Practise it
In your next few games, whenever two of your pieces stand on the same line, stop and ask: what would happen if the front piece moved? And do the same check for your opponent. Spotting the setup a move before it fires is what separates players who use discovered attacks from those who fall for them.