Thank you for your question, The forehead and scalp have an abundant blood supply, and injury to these areas often results in bleeding under the skin. When the bleeding is restricted to one area, it causes bruising and swelling. Doctors refer to this as a hematoma. Keep in mind that even a minor head bump can cause a large swelling. And the speed, momentum and size of the people and the forces involved (such as impact with a concrete floor or other hard surface) may increase the possibility of serious injury. Also seek emergency attention if : Persistent or worsening headache Imbalance Vomiting Memory loss Mood changes. If it was helpful hit thanks.