Well from my understanding of the the word nonviolent it means Nonviolence (from Sanskrit ahimṣā, non-violence, "lack of desire to harm or kill") is the personal practice of being harmless to self and others under every condition

As I see here is "under every condition" not allowing self defense. The rest is all good. On the other hand The non aggression principle is:

"No one may threaten or commit violence ('aggress') against another man's person or property. Violence may be employed only against the man who commits such violence; that is, only defensively against the aggressive violence of another. In short, no violence may be employed against a nonaggressor. Here is the fundamental rule from which can be deduced the entire corpus of libertarian theory."