I was about 13 years old and I had a single speed coaster brake hunk o junk. For whatever reason I was pulling a skateboard behind me on about 15' of rope. I happened to turn around and look just as the skateboard went under the wheel of a large 4X4. The skateboard stopped, the bike stopped, I didn't stop. When I finally got off the ground and went inside to get fixed up my mother had to use a pair of pliers to remove a rock from my shin bone. I still have the scar almost 30 years later.