Track an off-ball runner to deny the finish. Check the shoulder, pick up the blindside run early, stay goalside and touch-tight, and be first to the low cross to cut it out.
A wide player crosses low to the back post while an attacker makes a blindside run from deep. The defender checks the shoulder, picks up the run early, tracks it goalside and touch-tight, and cuts out the low cross. Emphasise scanning for the runner and not ball-watching. Vary the timing of the run and the cross. Rotate the defender and attacker.
Good runners arrive from where you cannot see them, which makes tracking a habit of looking rather than a burst of speed. By the time a defender has noticed the run, the attacker has two yards and the contest is over. Almost every goal scored from a late arrival in the box is a defender who was watching the ball and never checked.
The checking habit is small and specific: a glance over the shoulder every few seconds while the ball is on the far side, so the runner's position is known before he moves rather than discovered after. It costs nothing and it is the entire skill. Coaches can see whether it happened, which makes it something worth demanding rather than hoping for.
Picking the run up early is what makes staying with it possible. A defender who joins a run two yards behind is running to catch up rather than travelling alongside, and a runner who is being chased chooses where he goes. A defender who starts level dictates instead.
Goal-side and touch-tight is the position, and touch-tight is worth defining: close enough to feel him, not so close that a change of direction leaves you standing. Contact through the shoulder is legal and useful, since it tells you where he is without looking.
The last ball is the one to be ready for. Most of these runs are looking for a low cross or cutback, and the defender's final act is getting across in front rather than tackling from behind, which in that area is a penalty as often as a clearance.
Save it to your private drills, then change the animation, adjust positions, swap equipment, or drop it into a session block. Or start from a blank pitch and build your own.