A stand-your-ground law states that a person may use force in self-defense when there is reasonable belief of a threat, without an obligation to retreat first. In some cases, a person may use deadly force in public areas without a duty to retreat. Under these legal concepts, a person is justified in using deadly force in certain situations and the "stand your ground" law would be a defense or immunity to criminal charges and civil suit. The difference between immunity and a defense is that an immunity bars suit, charges, detention and arrest. A defense, such as an affirmative defense, permits a plaintiff or the state to seek civil damages or a criminal conviction but may offer mitigating circumstances that justifies the accused's conduct.
More than half of the states in the United States have adopted the Castle doctrine, stating that a person has no duty to retreat when their home is attacked. Some states go a step further, removing the duty of retreat from other locations. "Stand Your Ground", "Line In The Sand" or "No Duty To Retreat" laws thus state that a person has no duty or other requirement to abandon a place in which he has a right to be, or to give up ground to an assailant. Under such laws, there is no duty to retreat from anywhere the defender may legally be. Other restrictions may still exist; such as when in public, a person must be carrying firearms in a legal manner, whether concealed or openly.
"Stand your ground" governs U.S. federal case law in which right of self-defense is asserted against a charge of criminal homicide. The Supreme Court of the United States ruled in Beard v. U.S. (158 U.S. 550 (1895)) that a man who was "on his premises" when he came under attack and "...did not provoke the assault, and had at the time reasonable grounds to believe, and in good faith believed, that the deceased intended to take his life, or do him great bodily harm...was not obliged to retreat, nor to consider whether he could safely retreat, but was entitled to stand his ground."
In a Minnesota case, State v. Gardner (1905), where a man was acquitted for killing another man who attempted to kill him with a rifle, Judge Jaggard stated:
Justice Oliver Wendell Holmes, Jr. declared in Brown v. United States (256 U.S. 335, 343 (16 May 1921) a case that upheld the "no duty to retreat" maxim that "detached reflection cannot be demanded in the presence of an uplifted knife".The doctrine of "retreat to the wall" had its origin [in Medieval England] before the general introduction of guns. Justice demands that its application have due regard to the general use of and to the type of firearms. It would be good sense for the law to require, in many cases, an attempt to escape from a hand to hand encounter with fists, clubs and even knives as a justification for killing in self-defense; while it would be rank folly to require [an attempt to escape] when experienced persons, armed with repeating rifles, face each other in an open space, removed from shelter, with intent to kill or cause great bodily harm
