Blood spot under thumb where it got pinched. Do I have to do anything?

Subungual Hematoma. If you are having a lot of pain and discomfort as well, then you may need to see a doctor to have the collection of blood evacuated from under the nail. Usually this is done by poking a sterile needle through the nail to puncture it and allow the blood to drain out. Follow up with your doctor and have it looked at by a professional. Hope this helps.