ST. PETERSBURG, Fla. (AP) — The "stand your ground" self-defense law had been in effect in Florida for more than six years when it became part of the national vocabulary with the death of Trayvon Martin in 2012. When the 17-year-old was fatally shot, Florida was still one of the few states with the law that removes the duty to retreat before using deadly force in the face of danger.

Now, upwards of 30 states have some form of the law and recent research indicates they are associated with more deaths — as many as 700 additional firearm killings each year, according to a study published this wee...