Explanation

Basic ways to defend an attacked piece are running away to a safe square, blocking the attack, and protecting the piece. But sometimes none of these defenses are possible and the only way to avoid losing material is a counterattack or a check.

In the following situations a normal defense might not be possible and a counterattack or a check might be the best solution:

• More than one piece is attacked (see “Defend Against Double Attacks”): If one of the attacked pieces can make a counterattack or check, then each player has an attack.
• The attacked piece is trapped: A counterattack or check can move a piece out of the way and open an escape route for the trapped piece or deflect an attacking piece.
• The attacked piece is in a pin or skewer: A counterattack or check can move one of the pieces out of a pin or skewer, or deflect an attacking piece.
• The attacked piece must defend another piece or square: A counterattack or check can move the defended piece to a safe square or provide additional protection.

Similar situations can occur with intermediate checks and intermediate moves. Think of it like this: If you give a check or make a counterattack by moving one of your pieces out of an attack, the total number of attacks on the board increases by two in your favor.

If two of your pieces are attacked, then after the check or counterattack there is one attack on each side.

If each side has one attack, then after you give an intermediate check or counterattack with an intermediate move there are two attacks for you and none against you.

It can take a few moves of checks and counterattacks until such a situation is resolved. As chess grandmaster Yuri Averbakh put it, “The best way to meet a counterattack is often another counterattack.”

Examples

White has just attacked Black’s rook and bishop with a king fork. The bishop is also attacked by the knight, so 1...c6? or 1...Re5? lose to 2.Nxc5 (or 2.Nf6+).
The only defense is the counterfork 1...Rd4+ 2.Kxc5 Rxe4.

White sacrificed a bishop to pin the queen against the king but overlooked that Black can now defend with 1...Rf1+! to deflect the queen away from protecting the rook.
After 2.Qxf1 Qxd2 Black is up a bishop in the endgame.

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