NAP is an acronym for "Non-Aggression Principle." Sometimes it's called the ZAP, the “Zero Aggression Principle." Generally it means that one should not initiate force against another person. It does not address when or how defensive force should be wielded.
The NAP is not some intrinsic principle "out there" somewhere. Each person will implement it differently. If I call you an idiot, did I initiate force against you? If I say I intend to steal your stuff but don't, did I initiate force? If I threaten you, whether by displaying or not displaying a weapon, did I initiate force? These are all important questions for an individual because they will determine whether a likewise use of force is defensive or not.
So it's important to understand what the NAP actually is, in reality. Like all other motivations for a person, it is a choice. Those choices may arise because of upbringing, experiences, drugs, hypnosis or a million other causes, but still they remain a choice. This is what it means to live as a volitional being and no matter the causes of our volition, we are all that.
The NAP is a choice, a choice of the type promise. I decide (or don't) that I will treat others civilly and without forceful imposition. And of course, I either keep my promises or don't. Either way, the NAP is not something separate from ourselves, it is a decision of ourselves. Once this is recognized, along with the fact that some people do keep their promises, then a world of goodwill and production seems a lot more likely. We still only take care of ourselves, and at least we each do that.
" It does not address when or how defensive force should be wielded."
Gotta call bullshit.
At least as far as I learned.
It addresses something along the lines of "except in retaliation."
Defensive force is often instinctual or reflexive. Fight or flight.