I would agree with you there. If one were attacked from behind and knocked to the ground then pummeled by an assailant much larger than you, standing ones ground is no longer in the equation. It has now become a matter of survival........
"Stand your ground" presumes that you have an avenue of retreat. Mr. Zimmerman did not, he was on his back with his assailant on top of him......
Yep. Once you're overwhelmed with physical force, the option of retreat ins't available. It would be asinine for the law to assign a duty to retreat, to a person who is overwhelmed with force.