Explanation

Protecting a square is insufficient, if the protector can be forced away with an attack, leaving the square unprotected.

Let's look at the most common ways to remove a defender of a fork:

In this diagram, the black knight on b6 defends d7, preventing White from winning the b8 rook with the fork Nd7+. This defense is insufficient, because White can remove the defender in a few ways:

White can capture the defender of d7 with 1.Bxb6! This also captures the defender of the bishop on d5, so Black’s best response would trade that first with check: 1...Bxg2+ 2.Kxg2. However, after Black recaptures on b6, d7 is undefended; for example, 2...axb6 3.Nd7+.

Because the black knight is overloaded, White can deflect it with 1.Bxd5! If Black recaptures with 1...Nxd5, the knight no longer defends d7, and White can win with the fork 2.Nd7+. If Black tries a counterattack with, for example, 1...Bd6, White can just play 2.Bxb6 to win a piece.

White can also attack the defender of d7 with 1.a5, but here Black can play the counterattack to lose only a pawn: 1...Bxg2+ 2.Kxg2 Bd6 3.axb6 Bxe5 4.bxa7. That looks pretty good for White too, but the other options are much clearer.

Examples

Black just attacked White's queen with Rb6. Qd7+ would fork Black's king and rook, however the king is defending d7. White can win by attacking the defender with 1.Rc5+! Black has to play 1...Kb7, leaving d7 unprotected. White can now win a rook with the queen fork 2.Qd7+.

Sometimes attacking the defender can be combined with other motifs:

Black can win with 1...Bf5! The bishop attacks the rook, which is defending square e3. The bishop also clears the way for the rook on e7 to e3. After White runs away with the rook, for example with 2.Rxd6, Black can win a bishop with the rook fork 2...Re3+.

How to Spot an Opportunity to Attack a Defender

When you are threatening a fork, but the forking square is protected, always think about ways to remove the defence.

Related combinations

There are various ways to remove the defence. In addition to attacking the defender, other ways to remove the defence include deflection, and capturing the defender.