Greyhound racing. There is absolutely no reason why this couldn't keep going behind closed doors. There would be less than 50 people at the track. Social distancing isn't remotely a problem. No human would have to go without 2 metres of each other throughout the entire meeting. No jockeys racing like on the horses.
Likewise we could start the Cricket County Championship in April, with the usual 2 men and their dog in the crowd.
One day field spread out. (Obviously no standing up for the wicketkeeper
)
Non striking batsman runs on the next strip. Umpires stand back from the wicket, as bowlers bowl from an angle.