If a stranger attacks you inside your own home, the law has always permitted you to defend yourself. On the other hand, if an altercation breaks out in public, the law requires you to try to retreat. At least, that's what it used to do.
In 2005, Florida became the first of nearly two-dozen states to pass a "stand your ground" law that removed the requirement to retreat. If you felt at risk of harm in a park or on the street, you could use lethal force to defend yourself. The shooting of unarmed 17-year-old Trayvon Martin in Sanford drew national attention to these laws.