To Start Some Shiz?

straight left to the chin is a knockout

Bingo, it shakes the shit out of your brain. The chin moves when hit, which rattles your brain and at the least disorients the shit out of you.

I'd say a good hard hit to the sternum, although it is hard to hit the exact spot. Temple is the way to go and then juggular.

Or you can always shoot or stab him.