Having read all.of these posts I have a couple of comments. First I heard call 911. Most cellphones come with video cameras. A short documentary will avail you of cross examination.
Secondly I also carry a SD knife. Unopened it can give me certain advantages in a fistfight.
Third, I don't fistfight anymore. I used to frequent some stupid places. The last time I was in a bar a fight broke out and I hit the door because I had a wife and kids at home and really didn't havthe any business being there. The thought of the cops going to my house and telling my wife I was in the hospital or the morgue because I was at the bar didn't sit too well with me.
I am too old now too fight or run. An attack of any kind will put me in fear for my life. I would have to hit first and hit hard if it came down to it.
My second move would be introducing the BG to my gun. The choice would be his as to the next step.
As mentioned in several very good replies, when the time comes you'll know what to do. These are things no one can tell you how to react.