The DGU (defensive gun use) here was simply the peaceful act of carrying. But the DGU went horribly wrong. Lots of lessons — printing, retention, situational awareness, etc. But the salient take-away here is that there are some extremely irrational people walking around in public. This unfortunate armed citizen should probably get some more training for better concealment, among other things. Why? Because there are bad people out there — real criminals — who will take your gun to further their careers. There are also, as this gentleman discovered, nutcases who will forcibly remove a safely holstered gun and do violence with it, as some sort of political statement I guess.
Police said Smith was allegedly upset about another man carrying a concealed weapon. He took the gun away from the man, pointed it at him and another man, and shot the victim in the leg, according to the allegations.
I believe strongly in open carry, but open carry carries with it some added risk. You compensate for that risk in various ways. At a minimum, an open carry holster should have some type of higher level retention system to frustrate or at least slow down a gun grabber. You also should have some type of backup weapon to deal with that gun grabber. Pepper spray can be a good non-lethal weapon, useful in many encounters. But you may want to actually conceal a small firearm while open carrying. Sometimes, open carry is just not a good idea.