Unfortunately, this is an area in which there is a great deal of misunderstanding, which can have very serious results indeed..
First, the point of "stand your ground" laws and of court rulings of similar effect is simple: it is to relieve a defender of the duty to retreat from a place in which he or she has a legal right to be before using force to defend oneself. In common law, an actor had been required to show evidence that he or she had attempted to retreat, or that retreat had not been safely possible, before using force.
The "stand your ground" provision does not otherwise permit the use of force where such use would not otherwise be lawful, nor does it relieve the actor of the obligation to provide evidence that the use of force had been immediately necessary under the law. Those who oppose stand your ground provisions contend otherwise for the sake of argument.
The justification of the use of deadly force involves a particularly high threshold--reasonable belief that such force had been necessary for the prevention of death or serious bodily harm, and in many jurisdictions, the prevention of certain specified felonies.
One of the factors necessary in such justifications is evidence of a reasonable belief that the assailant(s) had had the ability to cause death or serious bodily harm. Usually, but not always, that pertains to the possession of a weapon.
The exception has to do with a disparity of force. That has been discussed here at great length. Use the search function, and read about the Larry Hickey case in Arizona. We need not go into it again, except to say that the fact that "a punch can kill" would be very unlikely to sway the triers of fact in a defense of justification.
