The Outsiders Theme

Does the book have a central theme?What does it mean?
The outsider is a teenage experience of a character who is a loyal to the people around him and will protect them at any circumstances. Throughout the story Ponyboy was not so stand up as he is in the intro of the novel. This weary character Ponyboy goes through beatings and losses of love one's as a the real average teenage gang member goes through. I think many of teens will find this book interesting because the main character stands out and comes almost to life as the literature progresses the whole theme of the book.