Sadly, this is a difficult one to back seat quarterback, because even concealed carry might not have helped him here. The guy sneaks up behind him and attacks without any noticed warning signs (The victim may have missed a lot of them, though, if he was in condition white).
Once he was cut, the guy walked away, turned and watched. If he shot him then (which I personally believe would be totally justified because the guy is still armed and not leaving), I can already hear the cacophony of Libs screaming that it was an unjustified shooting because it was damage already done and he could have tried to walk away.
Something similar happened in Austin years back where a homeless nut job walked down a crowded city street stabbing multiple people. Since he was just walking and sticking people and not screaming or anything else, it took a long time for anyone to really notice what was going on. People just started hurting, bleeding and wondering, "What just happened???"
I see this as a need for concealed carry
AND keeping your head in the game out there, which I will be the first to say can be difficult to do every minute of every day, but Condition yellow should be a constant thing once you venture out into the world.
