Please note that this is the Narutopedia's article on the technique used by Killer B. If you are looking for the article on the game-only technique used by Gengetsu Hōzuki then you should head to Headbutt.
After entering his four-tailed transformation, Killer B uses the two chakra horns that protrude out of his chakra cloak to headbutt the opponent. According to Sabu, this attack is strong enough to decapitate someone.
As with many of the techniques of Kumogakure ninja, this technique has an English name given kanji that somewhat match the pronunciation. Usually, the kanji would be pronounced as Atama Hattō.
Like Killer B's Lightning Release: Lariat, this technique is also called Killer B's eighth sword. Both techniques involve Killer B using the Eight-Tails' chakra to form horns.