Those people are still going to have social interaction. Why is that so hard to comprehend?
I understand your point. Truly. You're saying if they're not at a game, they'll go and do something else.
But they will have less. I guarantee it. Instead of bumping into 500 people it may only be 100. But when the rate of transmission is 1-5% per contact, that means they'll spread it to 0-5 people instead of 5-10. When more of the numbers are 0, we win. Doesn't even have to be all. Just more.
Especially if social distancing advice gets through to people. And believe it or not, huge cultural touchstones like movies/sporting events/concerts are not just vectors for contact, they're signals to the populace. People WILL take social distancing more seriously if they see big cultural organizations taking it seriously.
And that may be enough itself without quarantines. We'll see. But even if it's not everything, it will help flatten the curve.