He might get up and try to kill you or run, so while he’s on the ground holding his face from your knee, stomp with all your weight with one foot on his knee from the side.
Then he can’t stand or run.
When putting down a rabid animal, be safe!
I agree with the disabling the knee action.
Another way to be safe is to make sure that you have a round chambered.
The problem with a leg shot is that a man will bleed to death pretty quickly if you shoot him in the leg unless you have surgical precision or completely miss an artery. Even a 9mm will open up a leg pretty significantly unless it is just flesh.
And, you don’t want to do any life saving on a dirtball. And, if you are held liable the special damages (doctor bills lost wages etc) for a DOA are about 10% of what they will be for a survivor with one leg.
Shot put his brains on the wall. End of story.