Do not provoke, do not pursue
As I posted, as a armed citizen, you do NOT have the same powers or legal authority as a sworn LE officer.
If you can leave or "flee" a scene before it extends to a lethal force event you are required to do so(in my state).
If a aggressive subject is unarmed but may advance on you, you would be able to deploy a OC spray, Taser/C2 or impact weapon.
With the George Zimmerman hysteria going on, it's important to understand the use-of-force standards in your area.
IMO, many sheriffs & police chiefs could do a lot more to clarify what the legal standards-laws are but they avoid it for political-legal reasons.