I was driving to work one day and there was a bicyclist far ahead of me, alone.
I have no idea what happened but the gentleman flipped the bike and took a tumble right over the handlebars. No visible road debris, road wasn't wet, bicyclist wasn't doing anything silly.
I stopped and luckily he was fine (he was wearing a helmet) but seemingly for no reason, a bicyclist ate pavement.
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.
I have no idea what happened but the gentleman flipped the bike and took a tumble right over the handlebars. No visible road debris, road wasn't wet, bicyclist wasn't doing anything silly.
I stopped and luckily he was fine (he was wearing a helmet) but seemingly for no reason, a bicyclist ate pavement.