physics engine: ode, bullet, newton, opal (hate it), and if you use 3dsmax, reactor...
I'm not sure what you expect me to implement here - basically the only things that move are players and paintballs, and changing the behavior of either typically causes big upsets.
you wouldn't change the movement, you would be able make things like crates that fall over when you fly into them, and peoples bodies flailing around, past your head, right at you. its a GAME not real paintball, have you noticed you can jump 50 feet and live, not only that you can jump at 50 mph, ragdoll physics would be a sweet perk especially if the speed the bodies were moving at were overpowered. i remember last time i brought this up in irc, i was shot down and mutilated (so im very scared now).
P.S. maybe another feature where you can turn off ragdolls and go to animation that should make some people happier.