The term "extreme sport" usually refers to activities that involve a person getting on some sort of apparatus that allows them to move faster, jump higher, and fly through the air longer (e.g. BMX, motocross, snowboarding). But taking a unicycle off-road doesn't do any of those things. It's just really, absurdly difficult. As one guy says in the video, "The hardest thing is failure... literally falling on your face for ten hours." Ouch.
Indeed, we have a newfound respect for clowns. This looks hard enough—imagine doing it with a pair of floppy shoes.