HCA: Hermit Crab Association

Hello! New hermit crab owner here. I know that it is normal for hermit crabs to drop a leg if they are stressed or for other reasons, however my hermit crab that I got last week is missing the bottom part of his leg, rather than his entire leg. I just discovered this. Does anyone know potential causes for this?

Also I would love to post a picture of him but can’t figure out how.

it could have been caught on something, or been lost in an aggressive 'confrontation' -- he should grow it back during molting.