They can play sans fans. I suspect there will be huge limits to Assembly Hall, far more than football. I heard for football, B10 teams were told to prepare for 1/2 and 1/3 attendance maximums. My guess is outdoors, 1/2 might be possible but 1/3 more likely. I cannot see how basketball gets above 25%. I have been to a lot of women's games with 4000 people, it can happen with distancing but people have to be willing to. By nature, everyone wants packed into the side bleachers. The women do not use the balcony, which will have to happen to get 4000 in to a men's game. So people can distance at 4000, but will they is a different story.
I am not saying I would go to one of those games, but I think plenty of people would. At least 4000.
Now the experts are saying that 6 feet is not at all accurate. If that holds up, who knows.
But the most likely scenario I see is no fans.
Sans fans allows for TV contracts to stay intact which a Marketer will argue is even more valuable with the fans that were in arenas and stadiums having a high likelyhood of tuning in.