I saw it from seats on the backstretch, then went over to check out what it looked like behind the barrier afterwards. It is AMAZING that he did not kill himself... he hopped up on the top, on his butt, facing back towards the hurdles, then went over the back edge. It's a maze of aluminum supports behind the signage and padding, like you'd see as the framing for an exhibit booth at a trade show. And as said earlier, a good 10' or more to what appeared to be a concrete floor. Someone told me he grabbed part of the structure on the way down, I don't know how else he could have landed on his feet, he was headed for a landing on his back or head from the way it appeared. I have photo's from the jumbotron that they showed afterwards, his right arm is outstretched, appears he could have latched onto something on his way down.
Probably a better performance than his hurdles or LJ!