I ran across this succinct definition of the State by Murray Rothbard:
I define the state as that institution which possesses one or both (almost always both) of the following properties: (1) it acquires its income by the physical coercion known as “taxation”; and (2) it asserts and usually obtains a coerced monopoly of the provision of defense service (police and courts) over a given territorial area. An institution not possessing either of these properties is not and cannot be, in accordance with my definition, a state.
It seems a Homeowners Association established by some kind of perpetual contract (such as a restrictive covenant) that includes some means to collect revenue to pay for common expenses, which also includes the provision of a private contracted security force, could easily meet these criteria.
Is there a qualitative difference between such an HOA and a State?
It would seem that an anarchist society would need to avoid certain kinds of contracts to avoid gradually taking on the characteristics of a State. And these HOA contracts would fall into that category. What other kinds of things would need to be avoided?