If you wanna argue that Belichick is the best NFL coach ever, have at it. But arguing across sports? There's far, far too many differences to make any kind of reasonable comparison. My entire premise is that football coaches are, far and away, more important than in any other sport, at least the major US team sports, and if he's the best there, he has to be the best out of all of them. And your entire premise is ridiculous. I'm not diminishing his abilities, but, just to point out one flaw in this argument, he coaches FAR fewer games every year than coaches in every other sport. Again, just argue for him being the best NFL coach ever and be happy with that.