I'm not sure specifically which "motorcycle headbutt" story you are referring to. There could be various incidents involving motorcycles and headbutts in different contexts, like in a motorcycle race where a rider might accidentally collide and there could be a headbutt - like impact. Without more details, it's hard to tell the full story.
There could be a scenario where during a motocross event, a rider was taking a sharp turn at high speed. Another rider, who was perhaps a bit reckless, cut in too close. Their bikes collided in a way that one of the riders was thrown forward and his head hit the other rider's helmet in a sort of headbutt fashion. This kind of accident can be really dangerous as it can cause serious head injuries. And in some cases, it might not be an accident but a result of some unsportsmanlike behavior on the track. However, this is just one possible interpretation of a "motorcycle headbutt" story.