Why do we get a bump when we hit our head? i was playing basketball and hit my head against someone's forehead and now i have a bump that hurts.

Contusion/hematoma: Contusion is our fancy word for bruise while hematoma refers to a collection of blood. You can develop a bump anywhere you get hit but it's more noticeable on your head because your skull is so close so surface that swelling can't go anywhere inwards so it swells outwards as a bump. You'll notice soreness on your thigh for instance when hit there but no swelling per se b/c it's gone inwards.