I pretty much agree with all of you. If I knew in advance that a violent gang would be making an appearance, I'll strap a 300mm on my camera and climb a fire escape.
But what you'd be more likely dealing with is a small "mob" that quickly surrounds and turns on you.
Do they make pepper spray bombs? Something that would fog an area quickly. You get sprayed, but so do other 5 people getting ready to whip up on you.
I'm not afraid to use my camera as a weapon, but the flail went out of style years ago and for good reason. No control. When fighting multiple attackers, it seems like control would be important.
My thought was OC and my trusty knife. In a situation like that, you'd actually want the "fogger" type of OC. Hit them all at once. And if in the ensuing mayhem, someone gets close enough to be a threat, the knifes handle fills your fist for punches, and god forbid, the blade will end the fight quick.
I really need to put in that OC order, I've been meaning to do it for months now. This convinced me.