Explanation

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

The following diagram illustrates the most common ways to remove a defender of a skewer:

The black knight on h5 defends f4, preventing White from winning the b8 rook with the skewer Bf4+. This defense has holes, and White can win by removing the defender in a few different ways:

• White can capture the defender with 1.Rxh5! Now either 1...gxh5 loses a rook to 2.Rxf6+, or else Black trades rooks first with 1...Rxf1+ 2.Kxf1 gxh5, still leaving f4 undefended and letting White win with the skewer 3.Bf4+.
• White can attack the defender with 1.g4! Again, after 1...Rxf1 2.Kxf1 Nf6 (or Ng7) the square f4 is no longer defended and White can play the skewer 3.Bf4+.
• In addition to defending f4, the black knight is also protecting the rook on f6. The knight is overloaded. White can deflect the defender with 1.Rxf6+! After Black recaptures with 1...Nxf6, the knight no longer defends f4 and White wins with the skewer 2.Bf4+.

Examples

Qh8+ would skewer Black's king and rook, however the king is defending h8.
White can win by attacking the defender with Rg3+!
Black has to play Kf8, leaving h8 unprotected.
White can now win a rook with the skewer Qh8+.

Sometimes the attacking piece is the same which gives the skewer:

The unprotected rook on a1 is a clue for a possible skewer.
Black can win with Qh2+, attacking the king which defends h1.
The king has to escape to f1, leaving h1 unprotected.
From h2 the queen has access to h1, and Black now wins the rook with the skewer Qh1+.

Sometimes the attacked piece itself is pushed into the skewer by the attack:

This is similar to the previous example. This time the bishop on b2 is the unprotected piece.
Black can win with Qh1+, forcing the king onto the second rank, and away from protecting h2.
After Kf2, Black can win with the skewer Qh2+.

Visualization

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

Related combinations

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