Do a lot of people get subungual hematoma?

Yes: Very common after finger trauma.

If injured, yes: Subungual hematoma is a blood clot under a nail, usually from a direct blow (hitting your fingertip with a hammer, stubbing your toe). If you seek medical attention within the first 24 hours, they can be drained with a hot probe thru the nail - generally almost painlessly, and by relieving the pressure it really helps the pain! very small hematomas or older ones are not worth draining.