Crabs have pincers and not pinchers although the crab can pinch you.
The crab actually doesn't have separate pincers but instead the pincers the crab has are built into their two front legs.
When the crab needs to use the pincers they transform and quickly modify their two front legs into the pincers needed to ward off any predators.
The pincer claws that a crab has are used for a few different things such as gathering food for themselves and warding off any predators that may try to attack and eat them.
Most other predators will be fended off pretty easily with the crabs pincers but some may not and the crab still may get eaten.