Socrates,
In LE it's called the "use of force continuum". Same concept applies for non- LEs...you apply the type and quantity of force appropriate for the threat. Of course, sometimes if not most of the time, you have to adjust that "on the fly." You're trying to
stop the threat (key words) once you can't disengage.
Here's a simple example of continuum:
Disengage threat (get away) > verbal commands (Get back!) > empty hands defensive (push back) > less than lethal (OC, taser) > non-lethal offensive (punch/kick/martial arts/grappling/impact weapon) > display of lethal when warranted (draw pistol and issue command to cease and comply...be careful that you're not unjustifiably brandishing, a chargeable offense) > lethal force to protect life and stop threat
As an instructor friend says, "You have to have more than one tool in your toolbox." I carry a Surefire, a knife, a cellphone, and often, a Glock. As a civilian (non-LE most of the time, when not a reserve cop), I have a plan: be a good witness, avoid and/or disengage the threat, or escalate my reaction appropriate to the threat, bearing in mind lots of enderemployed lawyers and do-gooders who will try and hang you out to dry upon use of lethal force. That's always the last option.
Having about 4 yrs of mixed martial arts under my belt makes me realize the limitations of MA. I can handle certain situations, and simple joint locks and holds, and some defensive or even offensive maneuvers, are great when the drunk at the bar gets grabby, etc. But you never know who you're going against and what their intentions are, or how they are armed or trained. There are a lot of bad dudes out there, and even a lot of black belts have gotten their butts kicked by multiple assailants or a good street fighter, especially if armed. In Brazil, they had a rash of bouncers, all skilled martial artists, killed by BGs outside nightclubs. I always disengage when possible. You also have the liability: you tear into someone with your MA training, he falls and hits head and dies or goes into a coma after, or even just gets the losing end...who's gonna get arrested and/or charged, at least initially, when the cops come (and all his friends swear you started it!). Fighting is a last resort, at least now that I am older and wiser! And bear in mind that a big percentage of fights end up on the ground, and the guy who grapples best often wins. This is also a time when you might find yourself fighting to retain your CCW pistol when the BG realizes you have it, and he goes for it. Now he's armed when he wasn't before....dohhhhhhhh!
As an older guy myself (50), I realize the value of something I studied a bit under my Jujutsu sensei: combat cane. He taught the cane much like a short staff, and the hardwood canes (which you can carry anywhere, usually, iirc) are a formidable weapon in the right hands. The strikes, hooks, joint locks, throws, etc are amazing. I definitely want to study it again. (I wish we could legally carry ASPs). BTW, I am pretty fit, but I'm not 30 anymore to my dismay.
FWIW...random thoughts. Cheers.