If you think the police or judicial system, which the government is systematically dismantling, would even think about going to the extreme expense of positively identifying (say) 50 people in a crowd, then in each case building 50 prosecution cases that they felt could be proved beyond reasonable doubt, and then running 50 trials through the courts, all for singing songs (however vile) for which at best a slap on the wrist would be administered, you're dreaming. It's the sort of offence that a once-a-blue-moon occasional example is made but that's about it.
As for banning the 50 from grounds, dream on. The chances of your average turnstile operator positively ID-ing one of the 50 let alone refusing entry are about as close to zero as makes no difference.
Occasionally a sporting body might order a club to play behind closed doors for extreme racist chanting, but I can't imagine that ever happening in RL, and it doesn't identify let alone punish a single individual.
