I saw this on Animal Planet the other night. That was a three year old Gelderlander gelding named Jet. They were trying him out with an older gelding at that time.
What that video didn't show was the horse working fine a few minutes before. They walk and trot both ways, then stop right there. When they ask them to move on, something spooks the colt and he starts bucking. The driver said he was completly taken by surprise because the horse didn't show any tell tale signs of distress or that he was about to spook.
He actually kicked the driver in the temple and chin on the first kick and then in the chest before the driver jumped off. The next door neighbor, who was also a nurse said there was a perfect hoofprint on his chest. The driver was recounting the tale. He was truly surprised to be alive.
After that the horses were loose, with the youngster still bucking, the older horse just walks them into the fence.