What is Self Defense?
Self defense is difficult to prove or disprove as it is simply a matter of opinion and perception of a situation.  There are however, rules and guidelines applied to how self defense can be used from a legal standpoint.  In the United States and many other countries self defense allows anyone who is attacked to use reasonable physical force in their own defense and the defense of those they are protecting.  Self defense can range anywhere from vocal force to deadly force, depending on the situation.

Rules for Self Defense
While each state and jurisdiction varies in their specific guidelines and rules for the use of self defense, there are some general rules that apply.  Legal cases will make a distinction between physical force and deadly physical force.  The victim may use physical force to prevent imminent injury if logically they feel threatened.  Deadly force however, cannot be used on the attacker unless the victim is in reasonable fear of serious physical injury, or death.  In regards to defending family and friends that are directly involved in the situation, self defense extends to others who are at risk, in most cases.  This does not, however, include defending family or friends who are involved in illegal activities such as bar fights or street fighting.  Similarly, self defense cannot be used to aid a criminal in illegal activity.  In some countries and in the United States, “pre-emptive” self defense is legal.  This is legalized for the purpose of protecting the victim so that if they feel they are likely to be attacked they can get the first move, hopefully giving them the upper hand on the situation.  This must, however, be justified by a threat for imminent and immediate danger.

Self Defense and the Duty to Retreat
Some states have a duty to retreat statute in regards to self defense.  The duty to retreat statue requires that anyone attempting to use deadly force self defense on an attacker may only use it if they are unable to retreat safely.  Self defense can be used if the victim does not feel that a safe route is accessible in the situation.  This mostly applies to illegal fighting situations, such as being challenged to a street fight, where walking away is the best option.  The duty to retreat does not apply to those who are attacked in their own home, where the victim is not required to retreat.  In most cases, self defense should be used logically and as way to protect oneself from harm.