I think I may have discovered a much earlier depiction. Norm McLaren’s Neighbours was made in 1952 and prominently features a headbutt in a long fight sequence between the two main characters. The film was “mainstream” enough to have won several major industry awards in Canada, Britain, and the US, including an Academy Award for Best Documentary (Short Subject) (which is odd, considering the film is not a documentary). The film generated a lot of controversy at the time because of its depictions of violence; McLaren was forced to cut scenes from the film for its American and European releases. The film must have remained popular into the 1960s and 1970s, because according to Wikipedia McLaren was asked to restore the cut scenes due to a shift in public opinion during the Vietnam War. I remember the film being shown occasionally in the 1980s and 1990s on YTV and CBC.
Rocky features a head-but, but it’s in the context of a boxing match. In an early sequence, when Rocky is boxing in a club match, the opposing boxer head-butts him. This sends Rocky into a rage and propels him to victory.
Johnny Kwango was a UK pro wrestler who dated from the 1970s if not earlier - the head-butt was his signature move. Of course, this doesn’t necessarily establish its legitimacy as a worthwhile tactic.
While playing rugby in a games period at school, I got a bang on the head from my opposing prop as we engaged for a scrum, so I disengaged and let him have my forehead squarely on the crown of his. He folded up like a salted slug. Amusingly, the referee on the occasion was a very young Tony Spreadbury, now a top-flight international referee, who penalised the other side for charging into the scrum. That would have been about the worst decision he ever made, as my retaliation deserved an instant sending-off (and a ticket to see the headmaster, IMHO). He must not have seen it.
A British slang term for a head butt is a “Liverpool [or Glasgow] kiss” (probably every town in the country has a variation on this, though). The OED has the first reference to “Glasgow kiss” in the 1980’s. “Liverpool kiss” dates from 1944.
