UK authorities are running a number of control trials to research crowd transmission.
For instance this week they have allowed audiences at the world championship snooker in Sheffield. They started at about 25% capacity and the final is 100%. Each audience member is having 3 tests: the day before the event (lateral flow), on the day and 5 days later (PCR).
There have been other events tested across the world. I would expect that we should soon have a scientists’ eye view of the risk that crowded events pose.
Edit: a link to the testing site
https://www.gov.uk/government/publicati ... his-summer
Fortune favours the prepared; she has no favourites and takes no sides.
Truth is confirmed by inspection and delay; falsehood by haste and uncertainty : Tacitus