It’s not a nonsensical question, although it obviously does offend some sensibilities.
In the first place “fans are not necessary to the game”. The game exists, or could exist, without fans. I can’t count the number of athletic contests and games that I’ve played in that had no spectators whatsoever. “The game” doesn’t need them.
Obviously, for professional sports, we assume that paying spectators in an arena are a necessary element, else how would sports attract and retain such peak athletes in the prime of their physical lives? Not many people play games at that level “for free”, or for very long.
But we do have the Olympic model. Billions are spent on creating Olympic venues (which certainly include present live, paying spectators at those venues), but consider how many more billions are spent in broadcasting those Games to a far larger worldwide audience than will ever view them in person. So it’s possible that even high caliber professional sports could exist in some form with other kinds of remuneration / sponsorship / reward models. We just haven’t thought of that, yet.
It might also be possible to in some way limit the viewers’ attendance at a live event to below some as-yet-unknown critical mass point, below which an event of “fan violence” (assuming it doesn’t include weapons, arson and the like) would be no more than an unpleasant embarrassment, like a fight between parents at a Little League game, instead of a mass casualty event that spills over into widespread municipal rioting. In that way, live attendance at sporting events could be a total billionaires’ show, with only the team owners and selected fans – and relatively small numbers of them – in attendance, and the rest of the interested world watching on television.
Or maybe the fans just need to be armed, so that when rioting breaks out, they can start shooting the ringleaders. Or at least shooting at the ringleaders of the rioting on the other side. Hell, it could be a whole new endeavor for competition. Those Hunger Games aren’t going to start themselves, after all.