When you go to the game do you ever touch the seats, go to the toilet, touch the turnstile etc? All issues can be overcome but I'm sure the government's scientists will be advising there is a risk.
Plus, of course, everyone has to get to and from the games, and I'm sure not everyone will go straight there and back in a car. So increased numbers on public transport, in cafes and bars before and after the game, etc. Again, no significant extra risk *if* everyone behaves themselves, but that's proving to be a big "if" in most countries right now.