I loved this book when I was young...
To me, you can say that Rufus Henry is a hero because he overcomes many of his difficulties and looks like he is (by the end of the book) on his way to becoming something more than just another gang member.
At the beginning of the book, Rufus's major problem is that he has no hope. He thinks he could probably be something better than he is, but he really doesn't see how that can happen.
As the book goes along, he gets help from Alex Robbins and even from the football hero Ernie Brown. Between them, these two men help Rufus to think that maybe he can feel something other than hopelessness and fear.
Many of us never have to overcome anything so paralyzing as hopelessness and fear, at least not in significant aspects of our lives. Because Rufus is able to do that, you can say he's a hero.