Hello, Welcome to Just Answer and thanks for your question. The swelling may be lymph nodes swollen from draining the lymph system in the area. Swelling follows any form of infection or inflammation in the area of that particular lymph system. A hard hit to the head can cause a mild concussion and that really should be checked out by your medical provider. The swelling may be secondary to that, or not related at all and caused by some other infection or inflammation.
You're quite welcome. Good luck. I hope it is nothing but inflammation from the hit you took on Saturday.