Home advantage lives in the referee's ear

Crowd noise does less to the players than we assume and considerably more to the person making marginal decisions.

Empty stadiums gave the sport an experiment it would never have run on purpose, and the result was awkward enough that most people quietly changed the subject.

When matches were played without crowds, home advantage shrank. Not to nothing, but it fell, and the component that moved most was not shooting accuracy or distance covered. It was the decisions. Fewer bookings for the away side, closer to even on marginal calls, and less added time when the home team was behind. The players were much the same. The officiating drifted.

That is not an accusation of cheating and I want to be careful here. It is a description of how human judgement works under noise. A referee has a fraction of a second to rule on ambiguous contact, and ambiguity is resolved by whatever information is available, including a wall of sound arriving from thirty thousand people who have already decided. Under uncertainty, a loud consensus is a signal, and the brain treats it as one whether or not you want it to. The stronger the noise, the more it weighs on the calls that were genuinely fifty fifty.

Which is why the decibel peak matters more than the average, and why grounds with a steep single tier close to the pitch punch far above their capacity. It is not the volume over ninety minutes. It is the spike at the moment of contact. A sustained roar becomes background and gets filtered out. A sudden one does not.

The practical conclusion for a home crowd is unflattering but true. Constant noise is worth less than timed noise. The supporters who understand this instinctively are the ones who go quiet in a passage of play and then explode at a challenge, and their team gets more marginal decisions than a ground that sings the whole way through.

As for the fix, communication headsets and video review have already reduced the effect at the top level, and I suspect that is part of why some fans feel the atmosphere counts for less than it used to. They are not imagining it. One of the things the crowd was doing has been taken away from it.