Crowd noise is a load, and players pay it in the last twenty minutes

Sustained arena volume drains attention and balance long before anyone notices they are shouting to be heard.

Ninety minutes inside a loud enclosed arena is not simply unpleasant. It is a continuous demand on systems that also happen to keep an athlete upright and reacting, and the bill arrives late.

Start with the ear itself. The inner ear houses both hearing and the balance organs, and very loud low-frequency sound is one of the few stimuli that can nudge the balance side without anyone consciously noticing. In practice most players never register that. What they do register, if you ask them afterwards, is that they stopped hearing their teammates around the hour mark and started guessing. Guessing is expensive.

Take away reliable calls and a defender's decision moves from the ears to the eyes. He must turn his head to confirm what he would otherwise have heard, and a head turn while backpedalling is exactly the posture in which a player gets caught flat, plants awkwardly and rolls an ankle. The injury does not look acoustic. It looks like a bad step. Trace the sequence back and the missing information was audible information.

There is also a startle effect that I find underrated. A sudden roar behind a goalkeeper as a shot is struck produces an involuntary flinch, a fast trunk and neck response that costs a few hundredths of a second and shifts the head position from which he is tracking the ball. Once per match that is noise. Twenty times a match it is a genuine performance tax.

Then there is the vocal side, which nobody plans for. Talk over ninety decibels for two hours and a coach or a captain finishes hoarse, which is a soft tissue injury, just an unglamorous one. Shouting across a pitch in a dampened arena is easier than shouting in a bowl with a hard roof and long reverberation, and the difference is measured in how much of the second half a centre back can still organise.

Acoustic design is usually sold to fans as atmosphere and to broadcasters as clean audio. The interesting third audience is the twenty two people who have to keep processing in it. A bowl designed to hold and recycle noise for the crowd is also a bowl designed to bury the one channel of communication players cannot afford to lose. I would rather watch a defence that can hear.