Covid at the World Cup in Sochi

Knitted together from FIDE Tweets:

The FIDE World Cup organizers confirm that one of the players has tested positive for Covid-19. The result of this test was known while he was playing his second-round game. In line with the tournament's public health and safety protocol, the player has been asked to immediately leave the playing area, and his game declared a loss. The player in question was wearing a face mask during the game, and he has been placed in quarantine. His opponent, who was also requested to leave the playing hall immediately, will now undergo additional medical screenings and will be tested again tomorrow as scheduled.

this thead will get locked for sure

Why? What rule does this to bread break?