Tactics: Undermining (Removal of the Guard)

In chess, undermining is a tactic that involves capturing a defensive piece, leaving one of the opponent's pieces undefended or under defended. Undermining doesn't require a sacrifice for two reasons: 1) The defensive piece captured may be a loose piece not resulting in any recapture, 2) Your opponent may not choose to recapture even if it is possible.

• Every piece is capable of undermining.

The purpose of a successful Undermining Tactic is to:

1. Gain a material advantage.

2. Upset your opponent's defenses.

3. Set up a checkmating opportunity.

Below are several diagrams 
illustrating the undermining tactic.

A green colored box represents the Attacking Piece(s)
A blue colored box represents the Path of Attack
A red colored box represents the Target(s) of the Attack
A purple colored box represents the Undermined piece 

Diagram 1.1

(Black's queen has just captured white's D4 pawn...)

...And black was expecting white's 
queen to recapture black's queen 

Diagram 1.2

(White's response)

White capture's black's C6 knight and check's the 
black's king. Now black has to deal with this threat

Diagram 1.3

(Black captures white's bishop but...)

...now black's queen no longer has protection.

White captures black's undermined queen