Wheel could have gotten stuck in a recessed light rail line, pothole, or gouge in the road. A stick or shoelace could have become tangled in the front wheel and

Wheel could have gotten stuck in a recessed light rail line, pothole, or gouge in the road. A stick or shoelace could have become tangled in the front wheel and arrested its movement. For what it's worth, I did the same thing once without a helmet on (it was a rail line and my front tire got perfectly stuck) and made it through with only a scraped knee. So we're 1-1 on anecdata.