Self-Defense
Definition
Self-defense is a justification defense that permits the use of reasonable force to protect oneself from an imminent threat of unlawful physical harm. The force used must be proportional to the threat: deadly force is permissible only when facing a threat of death or serious bodily harm. In some jurisdictions, the defendant must retreat if safely possible before using deadly force (the duty to retreat), while others follow the 'castle doctrine,' allowing no duty to retreat in one's home. The defendant's belief in the necessity of self-defense must be both honest and reasonable.
Example
An aggressor advances toward the defendant with a raised knife. The defendant is justified in using deadly force because the threat of death or serious bodily harm is imminent.