Pretty much.
Yes, in a situation where there are three people, and there is only food enough for one, than the one who holds it is justified in using lethal force to defend it, and the other two are justified in using lethal force on one or both of the others in trying to acquire it. It is possible for people to be within their rights while having competing interests. Indeed, the incredibly grim situation is available for contemplation, that the “food” available IS the other person. We are made of meat, after all.
Alas, in such a brutal situation, brute force decides. If I’m better at killing you than you are at killing me, I win. That simple.
Indeed, I would need to do so, lest I lose the strength to in the future, and in any case, you’re eating the food I need while I wait. If I have a reasonable level of belief that no further aid or opportunities will come, that is a decision I may have to make.
No third-party arbiter, that is, someone not involved in this struggle for life and death, has any right to interfere. It is the dire necessity of imminent death which gives one the right to use the tools of death, and the third party does not have this.
What I’m seeing here is an argument from a utilitarian (which is bad) and collectivist (which is worse) place, that the non-aggression principle is best because it leads to the most smooth-running society (and one where rich people don’t have to fear being overrun by mobs of starving poor). It is overly simplistic and intellectually lazy. I think a better starting point is:
One may only act to harm another to the degree and in the way (physically, economically, etc.) that one would be harmed onself if one did not, and then only if no other means are available.
Just one sentence, albeit a long one. However, it covers both attack and defense.