Under Tex. Penal Code Ann. § 1.07(42), a reasonable belief is a belief that would be held by an ordinary and prudent person in the same circumstances as the actor.
This is fairly subjective. You give the question to the jury and let them decide what is reasonable under the circumstances. Like Churchill said about democracy, this is the worst way to decide things, except for all the others.
BOUNTY HUNTER: Any man who skips out on his bail can be hunted like an animal, although not eaten. All you gotta do is sit through a four-hour training course.
DALE GRIBBLE: You're telling me there's a poorly-trained, quasi-legal police force that operates with few, if any, government controls? IT'S ABOUT TIME!