Are there exceptions to the so-called "non-aggression principle," which says that it is never justified to initiate force against a peaceful person?

In some circumstances, could it be justified to use physical force on somebody that doesn't consent? What qualifies as "consent" in the first place?

This is part 1 of my breakdown of Episode 50 - my conversation with Stephan Kinsella. In the future, I'll release a second breakdown of our conversation about argumentation ethics.