CNN  —  Motorcycle racing is dangerous, of that there is no doubt. But within the sport there is one category that sits (bruised) head and (fractured) shoulders above the others. Supercross is a spectacular form of dirt-bike racing played out in stadiums, with wild jumps, eye-widening speeds and battling competition. Few riders embody the sport and its elements more than Austin Forkner, the most successful rider in the 250SX class never to win a title. The Missouri native has come close, but