If you want pain just screw up a parkour move, no protection at all, some guys just wear pants and shoes so your screwed if you stuff it up, it requires a lot of focus especially when you are running at full speed, even a slight misplacement of the foot can result in a lot of pain but technically parkour isn't a sport, it's more of a discipline so I interpret "sport" as an umbrella term for all activities. Also I think it's hard for some people to learn just because of the fear, mental barriers are a pain in the arse. Though ski jumping is probably the scariest, if you mess it up you are fucked.