Universities are a different question to tennis tournaments, though they share some similarities: mostly really young people, who often come from far and wide. But tennis has a few things in its favor: it is a relatively small group, and it has sway over its members: in that it controls their ability to work, their points, i.e., their income. If tennis and the players adhere to strict protocols, they might, JUST MIGHT be able to keep a tour running at a reduced level.
The notion is to keep players and their teams in tightly controlled bubbles, as much as is possible. Let's use the example of "Cincy" and the USO, because that's next up, and to be played in one venue. Everyone should be tested upon arrival in NYC, and then tested every time they arrive at BJKTC. If a player or a member of their team tests positive, they will be eliminated from the tournament and forced to quarantine in place for 14 days. (NOT fly to their home country and quarantine there.) If this happens to a couple of players during the course of the tournament, I think it can carry on. But there could be a point at which there is clearly an outbreak, if there is, and then the tournament would have to shut down. I hope this doesn't happen. I hope they get through this next bit in NYC relatively COVID-free, and move on safely to Europe.
This is why I think the turn-around to Kitzbuhel is too tight. If a player loses in the first week of USO, then opts to play in Austria, they would fly directly there and play. They could be exposed in NYC, or on the plane, and still test negative upon arrival in Austria. It can take up to 6 days, as I understand it, for a person to test positive. However, if NYC protocols are strictly observed, and Austria is likewise strict, they could mitigate the possibility of spread. From the USO, if the players who make the 2nd week go directly to their next tournament city and stay locked down, it might yet work. What they can't do is fly in and out, home and back, see friends, break the bubble, go to bars, etc. There is a pretty intense calendar of play for the men and women for the next while. If they adhere to a very strict and (let's face it) monastic lifestyle for the next while, they can play tennis, make money, and keep the tour viable. But they all have to be rowing the boat in the same direction. If you get some knucklehead like Zverev in the infamous video going out to the bars with friends, it could all collapse for everyone.