The gap that opens when the full-back follows his man

Milan against Venezia showed a small detail worth pausing on. Venezia used man-marking across the pitch. When Milan circulated the ball, the nearest defender followed his man all the way. That sounds disciplined. It also means one simple counter-movement creates a hole.

Musah dropped toward the ball while Cissé spun toward goal. His marker went with him. In that moment, the space between Venezia's second and third lines opened, not because of anything spectacular, just a runner dragging his man where the structure didn't want to go.

That is the thing to watch in the opening minutes. Not the ball. Where the markers are being pulled. If a full-back follows a winger inside, the flank behind him is empty. If a centre-back steps into midfield, someone has to cover the channel he leaves.

Look at the space a marker leaves, not the space he occupies.

Question: When a defender follows his man across the pitch, who is responsible for the zone he abandoned?