You can't even describe it as an accident. Because really, there was no way that was going to end without his getting badly hurt. A true future Darwin award winner right there.
What is especially funny to me is that this is probably the best outcome. Seriously, if the kid got both legs through, it would have been his chin on the rim. If the kid actually managed to get through the hoop without catching on anything, then he'd still have to deal with over a 10 foot drop to the ground. This caught him on his leg, and slowed his fall.