NFL will be the hardest of all sports to stage in the current situation even without fans because it requires the most people.
Each team has a 53 man player roster, at least 20 coaches, numerous assistants, trainers, doctors, etc. (Your normal NBA/MLB/NHL game has about 1/3 to 1/4 of that personnel wise.)
Then you add in all the referees, TV production people, security, stadium techs, etc.
Conservatively, that's @ 400 people in a stadium to stage a game. That's a boat load of covid tests you'd be chewing up. We're not currently in a place like South Korea or Germany are to be doing that. I hope things look better by late summer, but have no faith in our corrupt, idiotic government suddenly growing a brain.