Ariyan Islamian et al., "Chronic subdural haematoma secondary to headbanging", The Lancet 5-11 July 2014:
A 50-year-old man presented to our neurosurgical department in January, 2013, with a 2 week history of constant worsening headache affecting the whole head. He had no history of head trauma, but reported headbanging at a Motörhead concert 4 weeks previously. His medical history was unremarkable and he denied substance misuse. Neurological examination and laboratory studies, including coagulation screening, were normal. Cranial CT showed right-sided chronic subdural haematoma with pronounced midline shift (figure). He underwent burr hole evacuation of the haematoma and closed system subdural drainage for 6 days after surgery.1 His headache resolved and he was discharged home after 8 days.
Alvin Barnes, "Heavy Metal Headbanging is a Health Hazard, can result in Brain Bleed", Wall Street OTC 7/5/2014:
“We are not against headbanging,” said Dr Ariyan Pirayesh Islamian, one of the doctors who treated the man. “The risk of injury is very, very low. But I think if [our patient] had [gone] to a classical concert, this would not have happened.” [...]
Dr. Colin Shieff, a neurosurgeon of Headway, the British brain injury advocacy group, was of the view, “There are probably other higher risk events going on at rock concerts than headbanging”.
Islamian supported and quoted, “Rock ‘n’ roll will never die,” he said. “Heavy metal fans should rock on.”
The word headbanging and related terms like headbanger are a good example of the semantic quasi-regularity of English compounding. Even knowing that "headbangers" are fans of certain rock sub-genres, you might think that headbanging involves banging other people's heads, or banging heads with other fans, or whatever. But as Wikipedia explains,
Headbanging is violently shaking the head in time with the music, most commonly in the rock, punk and heavy metal music genres.
The same article includes a quote that illustrates the semantic focusing effect involved:
Ian Gillan, frontman of Deep Purple, when asked if he invented headbanging, said: "That’s a definite possibility", although he claimed that "it was not really head banging — more hair floating".
The OED has two earlier interpretations, with citations going back to 1886 and 1951 respectively, which
1. orig. Psychol. The action of repeatedly banging the head against something, or of repeatedly and violently nodding or shaking the head, sometimes accompanied by rocking of the body. Headbanging is fairly common in young children, esp. in the early stages of sleep. In older children and adults it may be associated with neurodevelopmental disorders and psychiatric illness.
2. Chiefly Polit. The action or process of enforcing cooperation or discipline among people in dispute or conflict. Cf. to bang heads together.