Originally Posted by Babaganoosh

Look at the size of American football players. Do you know how to calculate kinetic energy? Their size and speed is unmatched in any sport on the planet. The energy in which they collide easily breaks bones, hence all the padding. Rugby players are generally smaller. Less mass means less kinetic energy which means less potential for injury. The hits are infinitely less brutal and come from much smaller players which negates the need for padding.