Stab to the upper chest at a downward angle, probably hit the aorta. Guy was down in 10 seconds.
One: don’t get close enough to people in an aggressive situation where you can’t see their hands and have no time to react.
Two: a knife is a lethal weapon and you should have the right to defend yourself from a man with a knife with lethal force.
It’s not wrong or unfair to shoot a man with a knife when a man with a knife can put you in the grave in 10 seconds.