There are four elements to legitimate self-defense, and they must all be present simultaneously in order for there to be a situation where deadly self-defensive actions are warranted. They are:
3. Manifest intent (imminent jeopardy)
An "ability" is simply an injurious capacity. It usually manifests itself in the form of a weapon of some sort, but not always. Serious injury can be inflicted by many individuals using no weapon at all. The person you applied deadly force against must have been "able" to kill you or inflict serious bodily harm. Threats alone do not suffice, unless he had the ability in hand to carry them out.
If you were attacked by a person much larger than yourself, or by someone using martial arts techniques, or several individuals at the same time, you may reasonably conclude that he/they had the ability to seriously injure or kill you, even though they may have been technically "unarmed."
Disparity in size, age, strength, sex, and the level of aggressiveness of the involved parties are all important matters when considering the element of "ability."
When considering the element of "opportunity," we must have a situation where this attacker, in addition to having”ability," was also in a position to bring the destructive powers of his ability to bear effectively upon you.
The question is, were you within the effective range of his weapon(s)? For example, a knife or bludgeon is harmless in the hands of someone standing twenty meters away from you, [ or is it, in view of the Tueller principle]
yet either can be deadly if the person is standing within arm's reach, or is several meters away but closing fast. A firearm, on the other hand, is considered deadly at any range.