denying...

Denying the Opposition

Marking Marking and covering enemies ensures the prevention of their involvement into an attack. It usually forces the enemy attackers to move away from your goal by blocking their direct route to goal.
The two principles, on which playing defense is based, are compactness and quantity. In order to prevent the opposition from scoring, the defense has to be compact. They have to be closely packed and blocking the enemy's direct path to goal. This makes it harder for the attackers to develop direct plays and generally forces them to the flanks.
In the left diagram we see how the black team is marking their opposition man-to-man across the entire pitch. On a large scale, man-to-man marking is not very efficient in delaying the opposition. On the right-hand side, the black team pitches in a tight, close formation. The midfielders mark tighter and the fullbacks push forward, leaving the enemy forwards offside. Players on the opposite flank also pitch in. In this example, the right fullback and the right midfielder will have to communicate and be prepared to pick up any free opponent on their side in case he runs down the wing.
The second most important factor in playing defense is having advantageous numbers versus the offense. In football, defending 6 versus 6 is more favorable than 3 versus 3. The way to gain numbers is by always having your midfielders drop behind the ball. Therefore, the job of the fullbacks is to delay the enemy and give time for the midfielders to retrieve.

Clearing
Playing the ball out of danger is used to delay the opposition from advancing their attack. It should be applied when the enemy has built up momentum or when they have numerical superiority.