Angular momentum on the beach at Glen Brittle

Not me this time, although I enjoyed the sunshine on the beach at Glen Brittle on Skye in the summer. If you haven't seen the Danny Macaskill film where he cycles along the Cuillin Ridge, you really need to treat yourself. It's only 7 minutes long.  http://www.youtube.com/watch?v=xQ_IQS3VKjA After 6 minutes, he perfects a somersault onto the beach. The front wheel of the bike pivots against the fence. A force from the fence acts on the wheel to stop it. But that force is not inline with the upper half of his body, so that can't be stopped. It's momentum keeps his upper half moving forward. He's pivoted so it becomes angular momentum. I'll need to think about how he goes from having no angular momentum to some angular momentum. It must be due to an external torque acting (ie the fence). The angular momentum keeps him spinning until another external force acts - this time the beach. I ought to suggest that you don't try this at home!