Discovered attack (2 moves)
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A discovered attack can be especially strong if the discovering move is a forcing move, for example a capture, a check, or a second attack. In that case, the opponent often cannot handle that forcing move, and the revealed attack at the same time.
In this sense you can compare a discovered attack with a fork. For a fork, one piece makes multiple attacks. For a discovered attack, multiple attacks are made at the same time, but with multiple pieces.
Black can win with a discovered attack.
Bxf2+ sacrifices the bishop, which gives check, and reveals an attack by the rook on c8 on White’s queen.
No matter how white deals with the check, Black can capture the queen on the next move and has won queen for bishop.
In this case, the discovered attack is like a fork, in that two pieces (king and queen) are attacked with one move. The difference to a fork is that two different pieces are attacking: the bishop checks the king, and the rook attacks the queen.
White could give a check with Rc8+, discovering an attack by the white queen on the black queen. However, after Kg7 Qxd6 Nxd6 White would not have won anything.
Instead, white can win by capturing the queen's defender with Rxb5!, which discoveres an attack by the white queen on the black queen, and also protects the white queen at the same time. If black plays Qxb4, white can recapture with Rxb4, and the rook is no longer attacked. If black captures the rook with axb5, the discovered attack is decisive, as white can then capture the no longer protected queen with Qxd6.
Black can win with Bxf3!, discovering an attack by the rook on b8 on White's queen, and also threatening checkmate with Qg2#.
If White runs away with the queen, or captures the attacking rook with Bxb8, Black can deliver checkmate with Qg2#, as the queen on g2 would be protected by the bishop on f3.
If White proctects against the checkmate threat, Black can win the queen with Rxb4.
This works, because there is no way for White to defend against both threats at the same time.
Whenever a possible attack is blocked by one of your own pieces, think about ways to move that piece and make a discovered attack. If the discovering piece is of lower value than you'd gain with the discovered attack, your opponent will have to deal with the discovered attack first. You get a "free" move with the discovering piece, and can consider possible sacrifices. Giving a check with the discovering piece will often force the discovered attack to succeed. With some practice, you will be able to spot blocked attacks quickly, and grab your chance if a discovered attack is possible.
A discovered check is a move by one piece that reveals a check by another piece.
It is also possible to move one piece, revealing a threat by another piece that is not a direct capture,
but a checkmate or another tactic. This is called clearance.