see, in my head, when people say I should try mountain biking, I picture exactly that, with fewer spectators and more blood and broken bones. I'm not sure even the best gear in the world would improve my chances, I lose my balance just standing on my tippy toes (sober!).
Aside from having insufficient points of contact underneath their centers of gravity, i can't tell what caused most of those people to go arse over teakettle, other than perhaps going too fast on gravel (the turns at the end I understand, it was the straight downhill part I couldn't tell).