Is it possible that the person doing the tests, the medical staff not the player taking the test, had Covid at the time and has contaminated the players' tests? Mrs Colch tested our elder boy with an LFT when she was positive and it came up with a strong positive. Got him a PCR test and it was negative. The only thing we could think was that she had contaminated his test.
During the first year there was an outbreak At a sandwich factory in Northampton- loads were positive on PCR despite being negative on LFT - it was found to be contaminated during transit and about 30% of them were wrong
I guess with people faking negative tests to be able to go abroad or some faking positive tests to avoid work or school you could see people thinking sports teams would do something but imo the risk is far too great of them being caught