Are we talking Rugby vs. US Football?
I've never really played Rugby, but I have played full-contact USFB both with pads and without.
There's nothing like sending a dude a few yards down the field after a good pad to pad hit.
When dudes aren't wearing pads, I guarantee dudes hold back more.
When dudes are wearing gear, it's like a whole different mind set...
You feel kinda invincible in the gear....you can be confident that you can just SMASH the other guy and probably hardly feel anything.
Heh, this is gonna sound strange to most of you guys, but I used to train for body checks in hockey by skating full-speed into things like...I dunno...dumpsters...anything with mass that wasn't like a brick wall(it also helps that dumpsters don't dent like cars

)
I used to be able to move them several inches every time I hit them...lol.
~archi