What is the law on self-defense if the other person attacked you without any warning?

Every person is presumed innocent until proven guilty. Before you can be convicted of any crime, the prosecution must prove your guilt by proving all of the elements of the crime beyond a reasonable doubt. The burden is never on any defendant to show that he did not commit the crime. A defendant's only burden is to raise a reasonable doubt in the minds of the jury as to his guilt from all the evidence of the case. The defense of "self-defense" is what is called an "affirmative defense." When such a defense is raised by a defendant, the prosecution must not only prove each element of the crime beyond a reasonable doubt, it must also disprove self-defense beyond a reasonable doubt. While the law as to "self-defense" may vary from state to state, generally, a person is justified in using physical force upon someone else when it is necessary to defend himself or a third person from what he reasonably believes to be the use or imminent use of unlawful physical force by that other person. How much force is allowed to be used in "self-defense"? The degree of force which you reasonably believe to be necessary to defend yourself or another person from such unlawful use of force. Can you ever respond to an attack or threat of an attack by using deadly force? Deadly physical force may be used only if you reasonably believe a lesser degree of force is inadequate -- and you have a reasonable belief that you or another person is in imminent danger of being killed or of sustaining a great bodily injury. You are not justified in using physical force if you provoke the use of unlawful physical force by the other person. Nor will your use of force be justified if you are the initial aggressor, unless you have withdrawn from the encounter and effectively communicated your intent to withdraw to the other person, but the other person nevertheless continues the use of unlawful physical force. Also, physical force is not justified where is the result of an unauthorized combat by agreement.