Self-defense is a legal term that states a person who is under or is defending others when under immediate or imminent danger may use the force necessary to stop their attacker. In order to prove self-defense, there are certain standards/criteria one must meet:

• Imminent threat: one must reasonably believe that their life or other’s lives were in danger. Typically, a verbal threat is not enough, it would need to be followed up by some action that suggests harm. 
• Proportional force: the force used as defense must be equal to the threat at hand. For example, if the attacker hit you, and you responded with deadly force, it would constitute as proportional force. 
• Duty to retreat: originally, in order to plead self-defense, the person being attacked needed to attempt to flee in order to avoid violence. Though this law has been removed in cases involving non-deadly force in most states, the rule, in many states, still applies when dealing with deadly force. 
• Stand your ground laws: the “stand your ground” law essentially reverses the “duty to retreat” law. The law essentially allows for self-defense claims even if one does not try to escape in non-deadly situations. 
• Castle doctrine: the castle doctrine allows people to protect their homes against intrudes even if deadly force is necessary.