| Criminal defenses |
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| Part of the common law series |
| Insanity · Immunity · Mental disorder Diminished responsibility Intoxication · Infancy Automatism · Alibi Consent · Mistake Duress · Necessity Provocation Self defense False confession · Entrapment |
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| Law · Criminal justice |
In the United States, the defense of self-defense allows a person to use reasonable force in his or her own defense or the defense of others (see the theoretical background for why this is allowed).
While the definitions vary from state to state, the general rule makes an important distinction between the use of non-deadly and deadly force. A person may use non-deadly force to prevent imminent injury, however a person may not use deadly force unless that person is in reasonable fear of serious injury or death. Some states also include a duty to retreat (exceptions include Louisiana and Florida: see castle doctrine), when deadly force may only be used if the person is unable to safely retreat. A person is generally not obligated to retreat if in one's own home in what has been called the castle exception (from the expression "A man's home is his castle").
Runyan v. State (1877) 57 Ind. 80, 20 Am.Rep. 52, is one of the earliest cases to strongly support and establish in U.S. law an individual's right to initiate self-defense actions up to and including the justifiable use of lethal force against an aggressor.
In Runyan, the court stated "When a person, being without fault, is in a place where he has a right to be, is violently assaulted, he may, without retreating, repel by force, and if, in the reasonable exercise of his right of self defense, his assailant is killed, he is justiciable."
A related case is US Supreme Court Case John Bad Elk v. U.S. (1900) 177 U.S. 529, 44 L.Ed. 874, 20 S.Ct. 729, where a man was granted a new trial after being convicted of killing a police officer who was attempting to illegally arrest the man, because, at the initial trial, the jury was not instructed that it could convict on a lesser offense, such as manslaughter. Runyan v. State is further supported by additional cases such as Miller v. State (1881) 74 Ind. 1., Jones v. State (1888) 26 Tex.App. 1, 9 S.W. 53, 8 Am.St.Rep. 454, Beaverts v. State (1878) 4 Tex.App. 175, Skidmore v. State (1875) 43 Tex. 93.