To claim self-defense by legal definition in the state of Ohio, the defendant must prove three conditionals. With some exceptions, the defendant must prove that:
Condition 1, Defendant is not at fault
First, the defendant must not have created the situation. The defendant cannot be the first aggressor or initiator. However, in proving the victim’s fault, a defendant cannot point to other unrelated situations in which the victim was the aggressor. Remember, the focus is on the specific facts of the situation at hand.
If you escalate a confrontation by throwing the first punch, attacking, or drawing your handgun, you are the aggressor. Most likely in this situation, you cannot legitimately claim self-defense nor would you likely succeed in proving your affirmative defense
Condition 2, Reasonable and Honest Belief of Danger
Second, the defendant must have had a real belief that he was in immediate danger of death or great bodily harm and that his use of deadly force was the only way to escape that danger. Bear in mind that deadly force may only be used to protect against serious bodily harm or death. The key word is “serious.”
In deciding whether the bodily harm was serious, the judge or jury can consider how the victim attacked the defendant, any weapon the victim had, and how he used it against the defendant. Minor bruises or bumps from a scuffle probably do not meet the legal definition of “serious.” In court cases, rape has been determined to be serious bodily harm, as has being attacked with scissors. Serious bodily harm also may result from being struck with an object that can cause damage, such as a baseball bat or a wooden club.
The defendant’s belief that he is in immediate serious danger is important. The defendant’s belief must be reasonable, not purely speculative. In deciding if the belief was reasonable and honest, the
judge or jury will envision themselves standing in the defendant’s shoes and consider his physical characteristics, emotional state, mental status, and knowledge; the victim’s actions and words; and
all other facts regarding the encounter. The victim must have acted in a threatening manner. Words alone, regardless of how abusive or provoking, or threats of future harm (“I’m going to kill you tomorrow”) do not justify the use of deadly force.
Condition 3, Duty to Retreat
A defendant must show that he did not have a duty to retreat or avoid the danger. A person must retreat or avoid danger by leaving or voicing his intention to leave and ending his participation in the confrontation.
If one person retreats and the other continues to fight, the person who left the confrontation may later be justified in using deadly force when he can prove all three conditions of self-defense existed. You
should always try to retreat from a confrontation before using deadly force if retreating does not endanger yourself or others. If the person can escape danger by means such as leaving or using less than deadly force, he must use those means. If you have no means to escape the other person’s attack and you reasonably, honestly believe that you are about to be killed or receive serious bodily harm, you may be able
to use deadly force if that is the only way for you to escape that danger.
self defense is justifiable when the actor believes that such force is immediately necessary for the purpose of protecting himself against the use of unlawful force by such other person on the present occasion.
The Model Penal Code § 3.04(1)