You could definitely conduct a game of football with less than 50 people. Allowing for 16 players on each side, manager, coaches, referees and camera operators.
You could even test all of them ahead of the game, or even easier, just ensure they're all from low-risk groups.
As shit as it sounds, the only way to get this season done is behind closed doors. What it will need is the existing TV rights holders to do the right thing.