A person is justified in using force upon another person to defend himself against danger of imminent unlawful bodily injury, sexual assault, or detention by such other person, except that:
1. A person is not justified in using force for the purpose of resisting arrest, execution of process, or other performance of duty by a public servant under color of law, but excessive force may be resisted.
2. A person is not justified in using force if:
a. He intentionally provokes unlawful action by another person to cause bodily injury or death to such other person; or b. He has entered into a mutual combat with another person or is the initial aggressor unless he is resisting force which is clearly excessive in the circumstances. A person's use of defensive force after he withdraws from an encounter and indicates to the other person that he has done so is justified if the latter nevertheless continues or menaces unlawful action.