I'd personally be inclined to say that what you're doing when you resist my threat is contingent upon what kind of social arrangement we find ourself in.

In a Western-style parliamentary republic, your action will probably be interpreted as asserting property rights. If my intentions were obviously physically harmful, then we can throw in the self-defense, too.

But let's change the chair to something more consequential—a small crate of canned food. Let's say that you and I both know that you are not lacking for resources or food, and that I am homeless. And let's say that I steal this crate.

According to the interpretation of the NAP which takes property rights as a fundamental and does not admit of property already being an act of aggression in the first place, I'm the criminal, and you'll be in the right (maybe an asshole, but in the right) to resist my theft.

But assuming all the above, is it any more of an aggression to take your food (assuming I'm not off to stab you or whatnot) than for you to benefit from a societal interpretation of rights that threatens me with retaliation if I attempt to feed myself?