K (lightfalls)

One of the hardest things to do in a fight is to make it look like you're trying to kill someone without doing any permanent damage. They don't teach any half-moves in combat training. There are moves designed to kill and maim as efficiently as possible. If those are off limits, one option is open your fist right before a punch lands. Painful, but the force is distributed. Another showy option is a kick to the shoulder. You might break a rib or two, but if you aim right, nobody is going to the morgue.