I don't even have to show that it wasn't reasonable for Martin to have that belief because it was well demonstrated he didn't have any such belief. Because someone who had that belief doesn't call a girl living 180 miles away to shoot the bull, he'd call the police.
You should really familiarize yourself with the basic facts.
Martin was already on the phone when he noticed Zimmerman watching him.
Also, being on the phone with a friend does not preclude one from having a reasonable belief that someone else intended to use imminent unlawful force against them.
Nor does Florida law require that you must call the police as a suitable demonstration of that belief before you have the legal right to defend yourself.
And that's something you haven't even addressed, why did he call Rachel Jeantel instead of the police if he was in fear of imminent unlawful actions by Zimmerman?
Let's ignore for the time being that you have - once again - dishonestly conflated "fear" with "belief". Mostly, because it gets a little tiresome to point out every dishonest argument you make.
We'll also ignore the fact that you seem to be unaware that Martin was already on the phone by the time Zimmerman was following him.
So your question on its face is, at best, dishonest and ignorant.
But since you've already exhibited incoherence regarding your grasp of the basic and undisputed facts, let me expand on the chronology of events to see if we can enlighten you:
Martin walks home at night talking on the phone with his friend.
Zimmerman sits in his car watching Martin.
Martin sees him and runs away.
Zimmerman follows Martin.
Zimmerman makes no attempt to identify himself or announce his intentions.
Zimmerman makes a quick move for his pocket.
Hopefully, that will clear things up for you. If you are still confused about what happened and when, please let me know.
Now... in that exact scenario I just described, please explain how is was not reasonable for Martin to believe Zimmerman intended to use imminent unlawful force against him.
The jury believed that Zimmerman acted in lawful self defense.
It's weird that you presume to know what the jury believed.
Personally, I think I'd rather listen to the jurors themselves on that matter.
Here's what one of them had to say about it:
George Zimmerman got away with murder.
But of course your bizarre proclamations about what other people believe regarding the trial of George Zimmerman are beside the point.
We are discussing whether or not Martin criminally assaulted Zimmerman, and anxiously awaiting you to provide evidence of that crime.