to many to count. I live near a poorer neighborhood and there are always bike ninjas out at night.

the other day i put on my helmet before I went down a hill, a few moments later i had rode rash on my face, but not my head because I had on a helmet. When going at a slower speed you could in many cases brake your fall with your hands possibly protect your head. In my case I was going fast and although I put my hands out I couldn't resist the momentum and still ate the pavement.