Page 21 from Ohio CCW manual:
"The law specifically discourages citizens from taking matters into their own hands and acting as law enforcement agents. This is true even if the person thinks he is performing a good deed by protecting someone or helping law enforcement. The Ohio Supreme Court has rule that a person risks criminal charges if he interferes in a struggle and protects the person who was at fault, even if he mistakenly believed that person did not create that situation."
Whiccchhh means stay the fuck out of that situation of defending someone else. Additionally, you need to meet the 3 conditions to use deadly force: 1.) Duty to retreat, 2.) Resonable belief of harm, and 3.) Defendant is not at fault.
So, say they chick pulled up and started provoking, calling names to the 300lb dude. She is partially at fault. He beats the shit out of her, you approach and shoot his ass. Under the condition of "defendant is not at fault", you could be charged criminally for shooting him. Im guessing the guy with the gun heard 0% of the initial conversation, to determine who was at fault.