Goalkeepers stop shouting when the ground gets loud enough

Above a certain volume the voice stops working and defences fall back on hand signals nobody has properly rehearsed.

A goalkeeper commands his box with his voice. Keeper, away, step, mine. Those calls carry maybe fifteen or twenty yards over the ordinary sound of a match, which is enough, because that is roughly the size of the area he is responsible for.

Now fill the ground and put a corner into the near post at nought nought in a knockout tie. The voice does not carry fifteen yards. It might carry five. The centre-back at the far post is being spoken to by somebody he cannot hear, and he has to decide whether to attack the ball or leave it on almost no information.

This is why you see the collisions. Two defenders and a goalkeeper arriving at the same ball is not usually a failure of concentration, it is a failure of the communication channel, and the channel failed for a reason a decibel meter would explain.

What teams substitute is a set of visual conventions. The goalkeeper comes with both arms up and the defenders duck out of the way. The near post man raises a hand before the delivery to claim it. A shout replaced by a gesture. It works, but only if it has been drilled to the point of being automatic, and here is my complaint: it is drilled on a training ground where everybody can hear everything.

Rehearsing set piece defending in silence is rehearsing the easy version. A handful of clubs pipe crowd noise into training for this reason, mostly for atmosphere and mostly at a level that would not trouble anyone. Genuinely drilling the loud version, at match volume, with the calls deliberately unusable, is rare and I have never understood why.

Somebody will say players adapt on the day. They do adapt, and they adapt badly and expensively, and the adaptation shows up as the one goal from a set piece that decides the tie.

There is a wider point about away legs in famously hostile grounds. We describe the effect as intimidation, as if it were about nerves. Some of it surely is. But a large part of what a wall of sound actually does is disable the organising layer of a defence, and a defence that cannot talk is a defence of eleven individuals.

That is not intimidation. That is deafness, and it can be trained for.