Excellent capture! I don't have much to critique it on, but I love the dust cloud thats formed and it gives the photo a sense of movement compared to the frozen dirtbiker.
Irony is great, especially with the dust flying everywhere and the barb wire fence intended for "containment" behind it...makes it more of a statement like "let loose".
I myself, race motocross all over the US. To see these shots its very nice! It looks like you definitely knew what angles MXers are looking for... and thats tough love 'em!