In the context of a jury trial, SYG simply means that the defendant doesn’t have to back up or try to run away before using deadly force in self-defense. Formerly the defendant had a duty to retreat if he could do so safely. In many armed confrontations retreat is not an option, and the law prior to SYG allowed you to stand your ground in such situations. I don’t know many people who can outrun a bullet.
In the final analysis, SYG is more something for reporters and pundits to emote over than anything else. In many cases where you hear the media bellowing about SYG, it is a non-issue. Take the Zimmerman case for instance. Zimmerman’s defense was that he was flat on his back with Martin sitting on top of him beating him to death. If Zimmerman’s defense was true, under pre-SYG law he had no duty to retreat. Although a lot of ink was spilled over SYG in the Zimmerman case, it was really a non-issue for that case.
Having said all that, I feel compelled to close by saying I think SYG is a bad law because it gives people a license to kill in situations where killing isn’t necessary. I worked a lot of homicides in my 32 years as a prosecutor and defense attorney, and I saw lots of killings which were legally justified. I also saw lots of legally justified killings which could have been avoided if the killer had used better judgment. A justifiable homicide is not always a necessary homicide. SYG will increase the number of justifiable homicides which are not necessary homicides.
My advice to anyone is that if you’re attacked and you can safely retreat, do so. It may damage your self-image as macho guy, but it will save a life (maybe yours). In the words of a martial arts instructor I once knew “If somebody comes after you, walk away. If he follows you, run. If he catches you, kill him.”