I experienced my first OTB yesterday afternoon, more of a mechanical failure than rider error , although i think it could have been prevented. I was pumping up a hill on my #2 chainring fairly hard and right as I was coming up to a 5-6" tall rock that i needed to get over my chain popped completely of the chainring right as I was pushing down with my right foot. the lack of pedal resistance caused me to lean forward over my bars right as my front tire got to the rock(didnt get the chance to pop the tire up) and over i went. I broke my fall and kinda rolled out of it, but i hit my bars with both legs as a went over and have bruises right above my knees.