To pick nits: "Having a fear" isn't a good enough standard because some people are afraid of everything and everyone. Just because Jumpy Jane is afraid of all black people doesn't mean she can shoot every black person she comes across. There still has to be ability, opportunity, and jeopardy.
No, there does not have to be ability, opportunity, and jeopardy. Look in the use of deadly force statutes for any state and you won't find the words "ability," "opportunity," or "jeopardy." What you will find is pretty much what Brad cited from Texas law: "Fear of imminent serious bodily injury or death." I've seen at least one state that used the word "grievous" instead of "serious," but the intent is the same.
The way that plays out in not resulting in localized free fire zones around nervous Nellies is that the phrase is usually preceded by the word "reasonably," as in "the actor reasonably fears death or imminent bodily harm ..." What that means is, in court the shooter's story that he (or she) was in fear of death or serious injury is subjected to what the lawyers call the "reasonable man" test. All that is, is to have the members of the jury ask themselves if a hypothetical "reasonable man" would have had the same perception of fear under the same circumstances.
And because this determination depends on the totality of the circumstances, there simply can't be any hard and fast rule as to when you can or can't use deadly force to defend yourself. The best you can do is read the law in your state, understand it, and do your best to avoid having to test it in court.
