Indeed! The knee is a natural crumple-zone. Imagine if you roundhouse the back of the knee; if your reactions are a split-second off, they crumple, sandwiching your leg in their beetus bear-hug of a thigh/calf, which is no good: You're dead. And plus, it puts other shitlords at risk because, since you are human, others may stop to try to rescue you; like how you shoot to Injure in a war zone, not shoot to kill: Injure means 3 people are tied up trying to rescue the fourth. No good, puts too many humans at risk, not just yourself. Side of knee to crush their knee and hobble them: While the end goal of a hobbled fat pathetically crying while it watches the others escape to life like sands in an hourglass gives raging justice boners, truth is it's very hard to do: Knee is a lot harder to target in such a desperation situation (small target area, constantly in movement, it's like targeting a State Fair shooting gallery duck). Small of back is more reliable, less movement, etc.