[A] Common Law – A non-aggressor is justified in using force upon another if he reasonably believes that such force is necessary to protect himself from imminent use of unlawful force by the other person. However, the use of force must not be excessive in relation to the harm threatened. One is never permitted to use deadly force to repel a non-deadly attack.
[B] Model Penal Code – A person is justified in using force upon another person if he believes that such force is immediately necessary to protect himself against the exercise of unlawful force by the other on the present occasion. [MPC § 3.04(1)] In a departure from common law principles but in accord with the modern trend, a person may not use force to resist an arrest that he knows is being made by a police officer, even if the arrest is unlawful (e.g., without probable cause). [MPC § 3.04(2)(a)(i)] However, this rule does not prohibit use of force by an arrestee who believes that the officer intends to use excessive force in effectuating the arrest.
The provision does not specifically require the defendant’s belief to be reasonable. However, nearly all of the Code justification defenses, including the defense of self-protection, are modified by § 3.09, which re-incorporates a reasonableness component.
[A] Common Law – Deadly force is only justified in self-protection if the defendant reasonably believes that its use is necessary to prevent imminent and unlawful use of deadly force by the aggressor. Deadly force may not be used to combat an imminent deadly assault if a non-deadly response will apparently suffice.
[B] Model Penal Code – The Code specifically sets forth the situations in which deadly force is justifiable: when the defendant believes that such force is immediately necessary to protect himself on the present occasion against:
|2.)||serious bodily injury;|
|3.)||forcible rape; or|
The Code prohibits the use of deadly force by a deadly aggressor, i.e., one who, "with the purpose of causing death or serious bodily injury, provoked the use of force against himself in the same encounter." [MPC § 3.04(2)(b)(i)]
[A] Common Law – If a person can safely retreat and, therefore, avoid killing the aggressor, deadly force is unnecessary. Nonetheless, jurisdictions are sharply split on the issue of retreat. A slim majority of jurisdictions permit a non-aggressor to use deadly force to repel an unlawful deadly attack, even if he is aware of a place to which he can retreat in complete safety. Many jurisdictions, however, provide that a non-aggressor who is threatened by deadly force must retreat rather than use deadly force, if he is aware that he can do so in complete safety.
A universally recognized exception to the rule of retreat is that a non-aggressor need not ordinarily retreat if he is attacked in his own dwelling place or within its curtilage [the immediately surrounding land associated with the dwelling], even though he could do so in complete safety.
[B] Model Penal Code – One may not use deadly force against an aggressor if he knows that he can avoid doing so with complete safety by retreating. Retreat is not generally required in one’s home or place of work. However, retreat from the home or office is required: (1) if the defendant was the initial aggressor, and wishes to regain his right of self-protection; or (2) even if he was not the aggressor, if he is attacked by a co-worker in their place of work. However, the Code does not require retreat by a non-aggressor in the home, even if the assailant is a co-dweller.
The privilege of self-defense is based on reasonable appearances, rather than on objective reality. Thus, a person is justified in using force to protect himself if he subjectively believes that such force is necessary to repel an imminent unlawful attack, even if appearances prove to be false.
Courts are increasingly applying a standard of the "reasonable person in the defendant’s situation" in lieu of the "reasonable person" standard. Factors that may be relevant to the defendant’s situation or circumstances include:
|1.)||the physical movements of the potential assailant;|
|2.)||any relevant knowledge the defendant has about that person;|
|3.)||the physical attributes of all persons involved, including the defendant;|
|4.)||any prior experiences which could provide a reasonable basis for the belief that the use of deadly force was necessary under the circumstances.|
[A] Common Law – The traditional common law rule is that if any element necessary to prove self-defense is lacking, the defense is wholly unavailable to a defendant. Some states now recognize a so-called "imperfect" or "incomplete" defense of self-defense to murder, which results in conviction for the lesser offense of either voluntary or involuntary manslaughter. For example, a defendant who fails to satisfy the "reasonableness" component, although his belief was genuine, might be able to assert an "imperfect" or "incomplete" claim of self-defense, mitigating his crime to manslaughter.
[B] Model Penal Code – The Model Penal Code likewise recognizes an imperfect defense where the defendant asserts a justification defense, evaluated in terms of the defendant’s subjective belief in the necessity of using the force or other material circumstances. However, justification defenses are subject to section 3.09(2), which provides that when the defendant is reckless or negligent in regard to the facts relating to the justifiability of his conduct, the justification defense is unavailable to him in a prosecution for an offense for which recklessness or negligence suffices to establish culpability.
A special type of self-defense is the "battered woman syndrome" defense. Cases in which this defense arise may occur under three scenarios:
(1) "Confrontational" homicides, i.e., cases in which the battered woman kills her partner during a battering incident. In such cases, an instruction on self-defense is almost always given. It is now routine for a court to permit a battered woman to introduce evidence of the decedent’s prior abusive treatment of her, in support of her claim of self-defense.
(2) "Non-confrontational" homicide, where the battered woman kills her abuser while he is asleep or during a significant lull in the violence. Courts are divided on whether self-defense may be claimed if there is no evidence of threatening conduct by the abuser at the time of the homicide, although the majority position is that homicide under such circumstances is unjustified.
(3) Third-party hired-killer cases, in which the battered woman hires or importunes another to kill her husband, and then pleads self-defense. Courts have unanimously refused to permit instructions in third-party hired-killer cases.
[A] Common Law – Courts apply a transferred-justification doctrine, similar to the transferred-intent rule: a defendant’s right of self-defense "transfers" (just as intent to kill does) from the intended to the actual victim. While the defense is absolute in some jurisdictions, other courts do not treat this rule as absolute. If the defendant, acting justifiably in self-defense against an aggressor, fires a weapon "wildly or carelessly," thereby jeopardizing the safety of known bystanders, some courts hold the defendant guilty of manslaughter (or of reckless endangerment if no bystander is killed), but not of intentional homicide.
[B] Model Penal Code – If a person justifiably uses force against an aggressor, but uses such force in a reckless or negligent manner in regard to the safety of an innocent bystander, the justification defense, which is available to the person in regard to the aggressor, is unavailable to him in a prosecution for such recklessness or negligence as to the bystander.