Discovered Check and Windmill
What is a discovered check
A discovered check is a check that appears after one of your pieces moves off a line and opens up an attack by another piece.
Put simply: one piece makes the move, and another piece, which was blocked before, gives the check.
Discovered checks are most often given by a rook, a bishop or a queen, because they attack along lines. The piece that moves off the line is often a knight, a bishop or a rook.
What is a windmill
A windmill is a series of repeated discovered checks, where one piece keeps opening a line for another, and the opponent has to defend against check again and again.
Usually in a windmill one piece gives check, while the other uses the time to grab material. This idea is most often carried out by a rook with a bishop or a rook with a queen.
Why it works
The king is the most important piece. If your opponent is in check, they have to answer the check, not any other threats.
That's why a discovered check is often especially strong: you don't just open a line, you also force the opponent to spend a move only on protecting the king.
How to find a discovered check
- See whether one of your pieces stands between your long-range piece and the opponent's king.
- Check whether this piece can move off the line.
- Then ask yourself: who will give check after it moves away?
- Next, check whether the piece that moved can also create a threat of its own.
- If these checks repeat and you pick up pieces along the way, you are looking at a windmill.
Tips to spot the idea faster
For kids
Imagine one piece is standing like a "door". While it stays in place, the line is closed. As soon as it steps aside, a "laser" behind it switches on and hits the king.
If you can switch this "laser" on again and again, and grab pieces along the way, you get a real windmill.
For adults
Look for blocked lines of long-range pieces and check whether the piece in between can move away with tempo, that is, with a check, an attack or a capture.
A windmill appears when a series of discovered checks is forced and the defending side has no time for counterplay.
Examples
Try it yourself: make a move on the board. If you get stuck, press "Show solution".
1. Discovered check by a rook
Idea: the white bishop moves from e2 to c4 and opens the file for the rook on e1.
After Bc4+ the check comes from the rook. Any other bishop move off the e-file works too: the rook will give check anyway.
Solution: Discovered check: the bishop moved off the e-file, and the rook on e1 gave check.
2. Discovered check that wins the queen
Move: Nxc6+
Idea: the white knight on e5 blocks the file for the rook on e1. Wherever it goes, the rook will give check, so the knight can grab the queen on c6 along the way.
The opponent has to answer the check, so there is no time to win the knight back: White simply wins the queen.
Solution: Nxc6+ - the knight took the queen, and the rook on e1 gave check: Black has to save the king.
3. Windmill: rook and bishop
Moves: 1.Rxf7+ Kg8 2.Rg7+ Kh8 3.Rxd7+ Kg8 4.Rg7+ Kh8 5.Rxb7+ Kg8 6.Rxa7
Idea: the bishop on f6 is aiming along the diagonal at the king on h8, but the rook on g7 blocks its line. As soon as the rook moves along the seventh rank, the bishop gives check, and the king has to go to g8. Then the rook comes back to g7 with check (protected by the bishop), and the king goes back to h8: the f8 square is occupied by its own knight.
And it all repeats: in three turns the rook takes the pawn on f7, the bishop on d7 and the knight on b7, and then the queen on a7 too. Each time Black has only one possible reply.
Solution: Windmill: discovered checks by the bishop alternate with checks by the rook, and along the way the rook takes the pawn on f7, the bishop on d7, the knight on b7 and the queen on a7.