While I'd like to congratulate you for standing up for yourself, I also want to caution you to stop resorting to violence so much. Soon, you will get end up in a physical fight where you may cause actual damage to a person and end up held legally responsible, or face severe negative consequences. Worse yet, you may not win one, and be left forever scarred in a way that you may come to regret. Remember, as an atheist, this is the ONLY life you have to live. Try to live so that you never leave a sour taste in anyone's mouth.
If I were you, I'd start learning how to fight with words. Pick out Bible verses to use against this boy. My favorites are:
"Let he who is without sin cast the first stone." Jesus, as quoted in John 8:1 - 11
"Judge not, lest ye be judged." Jesus, as quoted in Matthew 7:1
You may even want to study up on sites like here and www.evilbible.com so that you are armed with knowledge of common misconceptions most Christians hold about the Bible, Jesus, and historical figures since that time.
You are a growing teenager. Your own strength is far greater than you realize. Also, you are only a few short years from being considered a legal adult, and even so, if you are shown to be a violent person, you may face adult charges of assault and/or battery even earlier. I've known 15 year olds who have been given life in jail, or sentences longer than they've been alive, for fights.
You do not want to throw your life away on people defending fairy tales. You want to show how much better your life becomes because you don't depend on an invisible friend to do the heavy/hard work for you. Work hard, keep your head straight and your nose clean.