Defending in soccer means you want to make your opponent's attack predictable so that you can apply the best possible defense in each third of the field.  In the defensive third of the field force the ball wide so that opponents have poor angles for shots on the goal.  In the attacking third and middle third force attackers to pass back to the middle of the field so defenders can anticipate passes and intercept them.  When an opponent becomes predictable they are much easier to defense.
Ken Gamble - August 2003