Two examples here:
Soccer players tend to undergo two situations that can jam their toenails, either scrapping them on the turf during the performance of an instep kick or having them stepped on, sometimes resulting in trauma that creates a blood pool underneath the nail and then the loss of the nail itself.
When I was teenager I cleverly stuck my foot under a moving car to settle an argument about whether it would crush my foot. Luckily the "it won't do any harm" brigade were right. It hurt less than having my foot trodden on in football games.