A distinct category of a strike which is physically distinguishable by striking with the front portion of the backs of the knuckles of the hand in a vertical direction.

Comments:

The vertical back-knuckle is called out from other back-knuckle strikes due to the contact points being the tips of the knuckles - where punches use the front of the knuckles and the true back-knuckles use the back of the knuckles.

Also, the vertical back-knuckle is also called out from the other back-knuckle strikes due to both the direction (vertical) and linear line of travel. In contrast, the other back-knuckle strikes are most typically executed on a circular path of travel.

One thing of note about this strike, is the bending of the wrist in relation to the target. It can be delivered with a straight wrist (like a high uppercut punch) or a bent wrist. This bend is effected based upon the directionality of the intended contact surface. For instance, if the intended target was the bottom of the jaw, then a straight wrist would be warranted. If the target was the philtrum, then a bent wrist would be more appropriate.