A low block is beaten by the second ball, not the first

Deep defences rarely fail on the cross itself; they fail in the four seconds afterwards, when nobody has a job.

Everyone rehearses the first contact. Two banks, distances set, near post covered, the header cleared. Watch the goals that actually go in against a deep block and most of them arrive after that clearance, from a ball dropping twenty yards out to a midfielder nobody picked up because everybody was busy defending the box.

The reason is structural. A low block compresses. To deny the space behind and inside, ten players squeeze into an area maybe thirty yards deep, and the moment the ball is headed away, all ten of them are in the wrong half of that area with their momentum going backwards. The attacking team has three players standing still at the edge of the penalty area facing the right way. That is not a marking failure. It is a physics one.

So the drill that matters is not the clearance. It is who steps.

Good deep sides nominate it. One midfielder does not defend the six yard box at all; his entire job is to stand on the D and be unhelpful. He loses his aerial duel by definition because he never contests one. He also ends most of the danger. I would rather have that player than a second centre back on the line, and I would say the same about a corner, where teams routinely put eleven bodies in the area and then act surprised when the recycled ball comes back with a free shot attached.

There is a cost and it is real. Leaving a man out means one fewer body against the first delivery, and if your goalkeeper is poor in the air you will concede some ugly ones. Fine. Concede them. The alternative is conceding cleaner chances from further out, and shots from the edge of the box arriving at pace, against a scrambling defence, are worth more than the average headed effort they replace.

The other thing nobody mentions about low blocks is what they do to legs. Repeated short decelerations, sideways, in a confined space, for ninety minutes, is a harder day than running forty yards in a straight line. Teams that sit deep for a whole season pick up a particular sort of groin and adductor complaint, and I have never seen a fitness department account for it properly.

Defend the second ball. The first one mostly takes care of itself.