Regarding fist fights...something I used to enjoy to a degree, when I was younger...
"Friendly" fights...some say they don't exist, but if that were true I wouldn't have lived past 18 or 20 (I'm almost 40). I won a few and lost a few back in the day...heck, the last one was just 5 years ago (I believe I lost...but he knew he'd been in a fight when it was over)...the fight started over a guy parked in the fuel island at a truckstop...he was in there for 45 minutes, busy truck stop, no room to back up and go to another island.
I was in a hurry and in a bad mood anyway...and when that guy walked out with his shower bag and wet hair...I lost my lil ole' temper. It was a pretty good brawl in the truckstop parking lot...lasted about 10 minutes...we were both pretty bloody, but nothing serious...we fought, got tired (sux getting old and out of shape), argued for a few minutes after the fight...then went our separate ways (I bet he thinks twice before parking in the fuel island again...whether he won or not)
I was armed (I always am)...but knowing it MIGHT end in a fight I removed my pistol before I jumped out of the truck and proceeded to cuss him like a dawg...he swung and missed and it was on!
I've been legally armed since I was 21...and have been in a scrap or 2 in that time (so sue me...I'm a redneck, can't help it, family tradition and all that)...I have never considered shooting somebody just because he was winning.
Granted that today friendly fights where a person only wants to prove his point probably aren't as common as they once were...but you shouldn't shoot a man just because he hit you with his fist...unless of course you have other problems that make getting hit life threatening (over 60 years old or various other handicaps).
But when you hear about people shooting people in road rage incidents, when both parties were physically capable of fighting....and one pulls a gun on the other (regardless of winning or losing)...thats just a coward!
Plain and simple...put simply its no different than 2 bucks fighting over does or or various other animals fighting over territory...they almost never kill each other, and when they do its mostly accidental...they fight, one wins, one loses, they go on with their lives.
I guess the point I'm making is this, and it may be off topic...but humans don't really seem all that smart to me...we can come up with all sorts of neat gadgets...but a simple common sense decision is beyond the grasp of most.
To answer the OP...if my family or myself is in danger, I'll act with extreme prejudice and fight as hard as I can right up until the life has left my body...If somebody is robbing the store (or the bank), they'll get no reaction from me if they don't pose a threat to the people I love...several decisions would have to be made on the spot based on what I saw.
Am I gonna be a hero for the bank or store...NO...not unless that is just a consequence of me protecting my family.