"In deciding whether T. Martin was justified in the use of force, you must judge him by the circumstances by which he was surrounded at the time the force was used. The danger facing T.Martin need not have been actual; however, to justify the use of force, the appearance of danger must have been so real that a reasonably cautious and prudent person under the same circumstances would have believed that the danger could be avoided only through the use of that force. Based upon appearances, T.Martin must have actually believed that the danger was real.
If T.Martin was not engaged in an unlawful activity and was attacked in any place where he had a right to be, he had no duty to retreat and had the right to stand his ground and meet force with force, including deadly force if he reasonably believed that it was necessary to do so to prevent death or great bodily harm to himself or another or to prevent the commission of a forcible felony.'
Martin, doing nothing wrong, was followed and confronted by an unknown, armed man.
You have the story scrambled. You put the end on top of the beginning. It is true that Zim was armed. But this was not known to TM before TM was shot. Would TM attack a man whom he knew was armed? I mean a "reasonably cautious and prudent" TM? I know, let's speculate on stuff we know nothing about. That'll get us to the bottom of it.
"Based upon appearances, T.Martin must have actually believed that the danger was real."
Fine. So he did. If that is the story you want proffer, then he both knew GZ was armed so he was entitled to defend himself with his fists; yet he didn't know that GZ was armed and the idea that GZ might fight back or defend himself is where the story kind of breaks down. If that is TM's justification (in your example) then it was he who attacked. He happened to attack a guy who was armed. And he lost that bet. Too bad.
Neither party loses their right to self defense, at any moment up until the time they are dead or rendered unconscious and unable to resist. Neither party has the right to throw a first punch at the other one.
If you are going to justify the use of force by TM, there is no way you can deny it to GZ.