I guess Christiano doesn't self test or self report. lolThanks for the link.
I'd say the big limitation is that the study relied on self-reporting to find out whether players have covid. Soccer players in the study had covid at a rate lower than the general population. And significantly lower at that. About 35% lower on a population of 90,000.
Either soccer is protective, or self reporting does a very poor job of identifying covid cases.