The stabber is not guilty according to the law of the jungle. Staring is a challenge in most of the animal world (humans included). I say the biatch had it coming.
In defense of the wimps, and in all seriousness:
You know what happens if one of you goes up to the guy and cold cocks him, and, God forbid, he barks his knuckles on the way down. Or to be closer to what actually happens: you see a knife and blood, you have an adrenaline dump, you knock the guy down, and in the throes of the adrenaline you hit him maybe one more time than is minimally necessary to render him not a threat.
Then, still drunk with adrenaline, you make unwise statements to him, as in "Do you need another, you son of a b*tch?" or to the subway police who interview you at the next station when the adrenaaline is still coursing through your bloodstream: "Sh*t NO, I wasn't afraid. I just had to get that b*sta*rd. People like that shouldn't be allowed in public." God help you if the perp is a member of a protected minority!
It is more true than ever that no good deed goes unpunished. You are guilty simply for being capable of defending yourself, and twice guilty if you exercise that capability - THRICE guilty if you exercise it on someone else's behalf, you vigilante, you ...
The left WANTS us to be helpless cowards.