Do head butts really work the way they do in the movies, where you can clobber someone by banging your forehead against his?
If so, why is the damage restricted to the victim, instead of the attacker sharing 50/50?
This question seems to get asked every 3 months or so. Have you tired doing a search?
I found this thread way back from 2002. It may have useful info, otherwise, someone who knows something may be along shortly. Link.
My WAG is that if you can whack your hard skull against something softer like a nose, the opponent takes more damage. But that’s just a guess.
Blake, I’m sure CookingWithGas is very sorry for cluttering up your pretty forum display with a desire to learn.
I was about to post the thread Inner Stickler just linked to. Having skimmed it over, the short answer seems to be it works as long as you hit them the right way (and with enough force), but generally that doesn’t mean hitting forehead to forehead. Forehead to nose or forehead to chin are suggested. At least one poster also mentions that it may depend on your relative tolerances to pain.
The key is that you get to choose what part of your head (the hard, upper forehead) contacts what part of your victim (somewhere softer, like the nose, face, etc.). If you headbutt someone right on the hardest part of their skull, it will hurt you almost as much as them.
I also learned from wrestling that the temple area of your head is much more sensitive than the forehead. During a match, one guy grabbed me and ground his forehead into my temple. I lost that match. That would also be a good place to headbutt someone.
It has to do with the angle at which the heads collide. If you (the butter) tuck your chin properly, and drive the crown of the head into some point on the mask area of the face, your head is going to move much less relative to your axis or rotation (which is roughly your spinal column). Thus the butter is less likely to suffer concussion than the buttee.
Hve a look at this clip (at around 2:10). Benitez has his chin tucked, Leonard does not. Benitez gets cut, but Leonard later said he spent the next couple of rounds trying to clear his head. Benitez tried the same thing again (at 5:23) but Leonard was able to avoid it.
Regards,
Shodan
I usually notice when threads recur, but I guess I missed this one the last 27 times. 
I had a thread about a baby the smacked me in the eye with his “baby fist” and he managed to give me a shiner, so I’m not sure it is entirely strength that matters.
Anyway other parents added that they had many injuries when they held their babies and suddenly the baby just moved their heads (back and front) and they 'caused injuries like bloody noses and such.
So if a baby’s head can give an adult an injury without effecting the baby, I’m sure an adult who knows what they are doing can do it too.
Even if the damage is divided 50/50, the butt-er at least has the element of surprise on his side - he’s ready for the pain, and the butt-ee isn’t. Useful if you want to stun a guy long enough to knee him in the groin.
When I was a kid I headbutted a much older and taller boy then me in the stomach and it was completely effective.