Ah, but it was a stand your ground case
in the sense that the jury instructions were stand your ground language:
Otherwise, self defense is rarely successful when the victim is unarmed, and a requirement for self defense claim is there is a duty to retreat from the dangerous situation.
http://legalinsurrection.com/2013/06/zimmerman-case-the-five-principles-of-the-law-of-self-defense/
The principle of Proportionality refers to the notion that the degree of force you may use in self-defense must be proportional to the degree of force with which you are threatened. Briefly, a non-deadly threat may only be countered with a non-deadly defense. A threat capable of causing death or grave bodily harm (e.g., a broken bone, blinding, a rape) may be met with deadly force.
Usually, the use of deadly force against an unarmed attacker is fatal to a claim of self defense. If you nevertheless wants to argue self defense you will have to convince the court that the unique circumstances warranted your use of deadly force despite the fact that the attacker was unarmed.
...
The principle of Avoidance refers to the notion that you should not use force in self-defense if you can avoid the need to do so by making use of a safe avenue of retreat.