What I read last night said internal bleeding. Yup, and it appears he had a dent in his forehead. He was having problems breathing when he got to hospital, punctured lung?
“problems breathing”
Can be a symptom from the brain:
“Most epidural and intracerebral hematomas and many subdural hematomas develop rapidly and cause symptoms within minutes. Large hematomas press on the brain and may cause swelling and herniation of the brain. Herniation may cause loss of consciousness, coma, paralysis on one or both sides of the body, breathing difficulties, slowing of the heart, and even death.”
https://www.merckmanuals.com/home/injuries-and-poisoning/head-injuries/intracranial-hematomas