Look, rugby players are tough, but drop the no-pads thing. Rugby involves tackling, NFL football involves HITTING. The difference is immense, as different as grappling and boxing.
If you want to talk about the hardest hitting team sport in the world, the discussion begins and ends with NHL hockey. No athletes run as fast as hockey players skate, and they HIT.
A big NHL collision is far more violent than anything a rugby player will ever see.
All these guys are tough, the pads allow for much harder collisions.