A defender facing a break with teammates behind him has two options, and the one that looks passive is usually correct. Delay buys the seconds that reorganisation requires.
Diving in resolves the situation the wrong way
A defender who commits to a tackle against a fast attacker either wins the ball or is eliminated entirely, and elimination leaves the attack in a two-against-one.
The probability of winning a tackle against a player moving at speed with the ball is not high, and the cost of losing it is a clear run at the defence.
Delaying converts an all-or-nothing decision into a manageable one, which is why coaches value it even though it produces no visible moment.
Retreating at the right speed is the technical part
The defender backpedals at slightly less than the attacker's speed, staying close enough to prevent a shot or a pass while never being beaten by a touch.
Moving too slowly allows a shot; moving too quickly means being run at with momentum and losing the ability to change direction.
Good defenders also angle the retreat, drifting towards a touchline so the attacker's route is longer and the available finishing angle narrows.
The clock is doing the defending
Every second of delay allows one recovering teammate to get behind the ball, and a counter that began three against two becomes three against four within a few strides.
The delaying defender does not have to solve the situation. He has to survive it long enough that it stops being a situation.
This is the reason coaches speak about defending as a unit even in moments that look like isolated duels.
Communication decides when to engage
The delaying defender cannot see behind him, so the players recovering tell him when they have arrived and when he can commit.
A simple call converts the duel from delay to press, and the timing of it is what turns a survived counter into a regained possession.
Where that communication is absent, defenders either commit too early or retreat all the way into their own box unnecessarily.
The skill is undervalued because it is invisible
Statistics record tackles and interceptions. They do not record an attack that fizzled out because a defender refused to be beaten for twelve seconds.
Some of the most effective defenders make comparatively few tackles, precisely because their positioning removes the need to make them.
Judging a defender by tackle counts therefore rewards the ones who allow situations to develop far enough to require a tackle in the first place.