Nice stop action. The picture seems a bit dark and OOF and the background is distracting. I would have cropped at the top portion of the tree trunk, so you didn't see any signs.
While this is a great action shot, and is appropriate to the subject, I feel that it is let down by being too busy (would have cropped a lot of the bottom off to remove the crowd and most of the signage), which would then make it a better picture. However I also feel that the light coming through the windows at the top distract from the picture.
I must admit that this is an original shot in this contest - I am not even going to think how the rider got there. The photo itself however has a few distractions and another angle more have yielded a better shot.
Good sports action! I would like to see more sharpness here, though to really capture the unbalance of the situation and to show the control of this biker over his bike.