Deadly force is generally defined as physical force which, under the circumstances in which it is used, is readily capable of causing death or serious physical injury. In order for deadly force to be justified there must be an immediate, otherwise unavoidable threat of death or grave bodily harm to yourself or other innocents. Deadly force is that force which could reasonably be expected to cause death or grave bodily harm.
The use of force is generally illegal unless it fits within the strict requirements of one of the four legal justifications. They are: self-defense, defense of a third person, crime prevention, and law enforcement. Each of these areas has specific requirements that must be met to avoid criminal liability. You may only use the amount of force that is reasonable and necessary in the situation.. This is judged by what a reasonable person would have done under the circumstances. In a self-defense situation, it is only when the aggressor uses or attempts to use deadly force that you have the right to respond with deadly force. Laws vary by state, so local law should be consulted for the applicable requirements in your area.
The following is an example of a state statute governing the use of deadly force to defend one's premises: