Spearhand strike
Nukite uchi, the spearhand strike, causes permanent debilitating injuries, so it must be practiced with the utmost care and attention. For this reason, it is forbidden to use spearhands during kumite. Spearhand strikes are thrown just like a front-foot or reverse punch, but impact is made with the fingertips instead of the seiken.
Goshin-Jutsu uses two variations of spearhand strikes: two-fingered, and four-fingered.
Two-fingered spearhand strike
Nihon-nukite uchi, the two-fingered spearhand strike, has only two applications -- to pierce the eyes or throat of your opponent. Two-fingered spearhand strikes are often performed with the lead hand as an atemi.
[video of a nihon nukie from the front and the side]
Some Goshin-Jutsu kata and waza use a "Three Stooges" variant of nihon-nukite uchi to strike the eyes. Some karate styles call this a snake-fist strike (hebiken uchi), since it resembles a snake's fangs. However, the Goshin-Jutsu version is performed with the palm facing upward, to prevent the fingers from buckling on impact.
[video of a "stooges" nukite from the front and the side]
Four-fingered spearhand strike
Yohon-nukite uchi, the four-fingered spearhand strike, is more robust and is used to attack soft tissues, such as the opponent's throat, solar plexus, abdomen, bladder, or armpits. Four-fingered spearhand strikes are often performed with the reverse hand to maximize power.
[video of a yohon nukie from the front and the side]
