Nukite uchi, the spearhand strike, is designed to cause 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
[Photo of a nihon nukite] [video of a nihon nukie from the front and the side]
Four-finger spearhand strike
[Photo of a yohon nukite] [video of a nihon nukie from the front and the side]