Thinking the Unthinkable

Well it was self defense I was in my own yard the 17 year old came at me with a fence poll he swung it at me and I hit him. Let me back up a bit though this whole thing started when I caught him leaving my garage with tools, I pressed charges on him for breaking in the garage, about 3 days later he attacked me with the pole. I hit him and his grandmother pressed charges on me! We had a court date during court my lawyer informed me I will not go to jail if I drop the charges of him braking into the garage, because the grandmother will drop the charges of me hitting him. So we both dropped the charges. If it was legal to defend yourself against a minor why did I spend 3 days in jail? Never been in any trouble before except for that, not even so much as a speeding ticket.