Self-defense is a defense to certain criminal charges as well as to some civil claims. Under both Criminal Law and Tort Law, self-defense is commonly asserted in cases of Homicide, Assault and Battery, and other crimes involving the attempted use of violence against an individual. Statutory and case law governing self-defense is generally the same in tort and criminal law.

A person claiming self-defense must prove at trial that the self-defense was justified. Generally a person may use reasonable force when it appears reasonably necessary to prevent an impending injury. A person using force in self-defense should use only so much force as is required to repel the attack. Nondeadly force can be used to repel either a nondeadly attack or a deadly attack. Deadly Force may be used to fend off an attacker who is using deadly force but may not be used to repel an attacker who is not using deadly force.

In some cases, before using force that is likely to cause death or serious bodily harm to the aggressor, a person who is under attack should attempt to retreat or escape, but only if an exit is reasonably possible. Courts have held, however, that a person is not required to flee from his own home, the fenced ground surrounding the home, his place of business, or his automobile.

A person who is the initial aggressor in a physical encounter may be able to claim self-defense if the tables turn in the course of the fight. Generally a person who was the aggressor may use nondeadly force if the victim resumes fighting after the original fight ended. If the original aggressor attacked with nondeadly force and was met with deadly force in return, the aggressor may respond with deadly force.

Courts and tribunals have historically accepted self-defense as a defense to a legal action. As a matter of public policy, the physical force or violence associated with self-defense is considered an acceptable response to aggression.