Answer

This is most like an Aural Hematoma. This is a condition where the flap of the ear fills up with blood due to damage to the blood vessels inside. The most common cause is excessive scratching or head-shaking, often due to an underlying ear infection, allergy, or other irritation. The usual treatment is to control the underlying problem if possible, and then to do one of the following for the hematoma:

Surgery is the older approach to fixing this - the ear is cut and the clotted blood is scooped out. The ear flap is stitched back together to prevent filling up again.

The other approach is medical - start steroids such as Prednisone for 4 to 6 weeks, and optionally, drain the fluid from the hematoma. It often refills in a short period of time, but the body will reabsorb the fluid eventually.