Defend the cutback. Recover to the danger zone as the ball reaches the byline, read the pull-back, and get across the line of the cutback in front of the striker to intercept, block, or clear.
A winger drives to the byline and cuts it back for a striker arriving at the penalty spot, defended by a defender and keeper. The defender drops into the cutback zone, reads the pull-back, and steps across in front of the striker to intercept or block, then clears. Do not dive in on the winger, protect the cutback line. Rotate roles and vary the delivery.
Everyone follows the ball to the byline and nobody covers the space it is about to be pulled back into. That is the whole reason cutbacks convert so well, and it is a positional failure rather than a technical one. The defenders are not beaten by skill, they are looking the wrong way.
The zone that needs occupying runs from the penalty spot to the edge of the box, and somebody has to be dropping into it as the ball reaches the byline rather than after the pull-back is played. By the time the ball is travelling backwards it is too late to recover into that space, because the attacker arriving is already at full speed and facing goal while the defender is turning.
Which defender takes it depends on the shape, and the answer needs deciding in advance rather than being improvised. Commonly it is the far-side centre-back or the holding midfielder recovering, but a team that has not agreed it will find all four defenders in the six-yard box and the cutback zone empty.
The individual skill is feeling the runner without watching him. A defender who turns to look at the attacker behind him loses sight of the ball; one who watches only the ball gets beaten by a run he never felt. A shoulder check as the ball approaches the byline is enough to know where the runner is, and after that the ball is the priority.
Getting across the line of the cutback in front of the striker is the intervention. Blocking it, intercepting it or clearing it are all acceptable, and it should not be a tackle.
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.