Biggest problem is they don't have an explanation for the trend "reversing". If the hypothesis referee bias in front of home crowds is the main factor is correc

Biggest problem is they don't have an explanation for the trend "reversing". If the hypothesis referee bias in front of home crowds is the main factor is correct, home and away card allocations should follow the same pattern within a small margin of error in the absence of crowds, not reversed with sometimes greater magnitude. Most obvious reason for away teams committing more fouls per booking in an empty stadium is tactical: away teams are often set up to defend more, in a well structured manner, which means the ratio of inconsequential fouls vs cynical fouls to stop the counter attack, massive misjudgements and losses of temper is likely to be higher This is compatible with the hypothesis that a 'biased' ref is less likely to let a side get away with regular inconsequential fouls when the fans are screaming at him. But it's also conceding the very large role played by tactical approaches which stats suggest have also changed since the pandemic