exact same thing happened to me during a mountain bike race last year in mile 1 of a 16 mile race. I came down hard on the nose, which caused the binder bolt to break off (the post was 10 years old, btw) so I removed the rest of the post and did the whole rest of the race standing up. Fortunately I could pull it off because my MTB has a sloping top tube which left me with plenty of clearance. Not sure if I'd try the same thing in a 'cross race though. on one hand since I started singlespeeding, I have been standing most of the time anyway, but on the other hand, my CX bike has much less clearance.