I wrote this essay, and Don Rearic helped me in the editing and added some important details. I was writing this for my Jujitsu teacher after we had a discussion about justifying deadly force. After Monday's class I whipped out my criminal law book and summarised the section on self-defense.
Without Further Delay:
A first point to remember is that self-defense is considered a justification for using force. It is a defense to a criminal charge such as assault, battery, assault with a deadly weapon/implement or murder. In response to one of these charges the defense would be to plead not guilty and claim self-defense.
As a justification, it has good points and bad points. A good point is that if you can explain what you did was reasonable, you walk away. A bad point is that you have to say you did it, but you were justified in doing it. That precludes you saying that it was not you that did the deed.
In a criminal case, the prosecution has the burden of proving what they consider to be the illegal, criminal or overzealous nature of the offence beyond a reasonable doubt, almost to the point of 100% proof. The legal defense of Self-defense, in contrast, requires the defendant only to prove its case to a preponderance of the evidence, just over 50%.
A model set of requirement for Self-defense as a viable, legal defense is:
1 The defendant believed physical force to be necessary for self-protection;
2 the belief is based on reasonable grounds,
3 the force used was necessary to avoid imminent danger,
4 the force used was not in excess of that believed necessary to repel the unlawful attack.
Another requirements is that the defender must not have been the one to start the fight. For instance, A cannot go up to B, assault B, and when B responds, and A fights B off, A can not claim self defense as justification for the injuries he gave B while fighting B off, unless B, the assaulted person in question, used excessive force and A can prove that. This is another difficult case that will no doubt be handled on a case by case basis and nothing will be written in stone.
Non-physical provocation is never answerable by physical force. Verbal assault does not allow a person to respond physically, unless accompanied my an action that is threatening. For example, A says Im going to kill you!! then A reaches into his car for something. In that case As words give weight to his actions and may represent an immediate threat. See requirement 3 above.
People also have no right to use force against an arrest made by a police officer, even if the arrest is unlawful. That is from the Model Penal Code, and may not be valid in all states, but its likely that it is.[ ]
Deadly force is not justified if the actor can avoid the necessity of using deadly force by retreating with complete safety. This is the infamous Duty to Retreat statutes in some states. Note its complete safety, that means you dont have to run if you feel you will not be able to escape the attacker, you have to defend someone else, or in most cases, in your home. A good example of retreat with complete safety is if you are seated in your vehicle and someone approached your vehicle and was obviously hostile, dont bother staying around if you feel in danger, simply drive away. Exiting the vehicle to confront them would make you an active participant unless there were other circumstances. If the person approached with a firearm in plain view and you were carrying a firearm, you also may be able to engage with your weapon instead of fleeing if it is clear that fleeing instead of neutralizing the person making the approach, you could be killed or suffer grave, bodily injury.
Another point to mention, if carrying of a weapon for self defense in violation of a states law prohibiting such a weapon, and the weapon is used reasonable and lawfully for self defense, the justification of Self-defense is unlikely to affect the charge of carrying the weapon itself. For example, Nunchaku are illegal in MA, yet if used to defend yourself lawfully with them you may still be charged with their possession and illegal carrying/concealment of them.
States have varying weapon laws for firearms and non-firearm weapons. Some states allow citizens quite a variety, others are quite strict. MA, for example requires a permit for pepper spray, and it may be illegal to carry a kuboton in MA as it is a martial arts weapon.
Now to pick apart the four requirements I listed above. #1 is linked with #2 and there application is very simple. The defender must reasonably believe that physical force is necessary for their protection.
The reasonable part is the difficult part. What is reasonable to you may not be reasonable to me, and what we can agree upon may be different to someone else. The basic set for a two handed front choke may is likely to be reasonable to most people. Hitting someone in the throat with an edge of hand blow for grabbing their arm may not be depending on the circumstances. For example, if two men similar in size were the attacker and defender, this might not be reasonable. If the attacker grabs the defenders arm and then tried to draw a weapon and was actively trying to control the defender, then the rules change. Also, simply unarmed, if a man grabs a womans arm and it is clear that he is going to try to drag the woman to a waiting vehicle or a secluded area, like a stand of trees on the periphery of a parking lot, clearly for the purpose of kidnap and/or rape, the woman might very well be able to use lethal force against an unarmed attacker who outweighs her, etc.
Next, point three, that physical force may only be used to avoid imminent attack is important in that it limits the time frame when physical Self-defense may be used. The justification of Self-defense only protects a person against imminent danger. Responding to past or future danger is revenge or a Pearl Harbor style preemptive strike. Self-defense does not preclude striking first to avoid an imminent assault; it only precludes striking first when no danger is imminent. For example, If A approaches B stating A is going to rip out Bs______, and it is reasonable clear A is going to assault B, and B then hits A in the jaw with a jab-cross combo it would most likely be interpreted as reasonable because B was in fear of great bodily harm or death and although A did not actually assault B, the danger was imminent, and the fear reasonable.
The fourth point, that the force used should not be in excess of that believed necessary to repel that unlawful attack is simple in application. Once Mr. Bad Guy is no longer a threat to you, please stop hurting him. If A tries to punch B, and B responds with a block and a palm-strike to the face, edge of hand blow to the neck and a knee to the groin, then A falls down, B has used the force necessary to repel the unlawful attack. A finishing kick or hand blow after a throw incorporated into the technique would not be a shot just for the hell of it, but a legitimate technique to insure the defenders safety. If B then decides to give A one more kick for good measure, B is now unlawfully assaulting A.
Comments or questions invited.
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. If it gets dirty (germs..yak!), I'll just toss it and get a new one. Those germs are enough to break all the emotional bonds..and of course I clean off my fingerprints too, and get rid of the tool and cloth. Maybe I should just ask the mugger politely if he has HIVs in his blood (That could be considered murder, LOL). I'm mean, nasty and tired, so I'll head to bed. Thanks for the idea -- I'll sure keep it in my mind! 
