Rugby is a very different sport. Large portions of what happens in an NFL play, perfectly legal with the rules stuff, is against the rules in rugby. They just don’t run at each other as much, there’s not as much emphasis on bringing people to the ground. Football is a collision sport, rugby gets some collisions but that’s really the point of football.
Plus in rugby, head hits (both using the head and going for the head) are, as far as I know, illegal and grounds for ejection. Too many football players were taught to lead with the head, or tackle in a way that caused head-to-head clashes. There’s no helmet in the world that can prevent effects from those building up over time.
The sport that causes me to be amazed is Australian Rules Football. Those guys jump like basketball players and hit like American football players...with no pads at all. I wonder if they have similar concussion issues to the NFL/NHL, because man, those guys HIT.