The answer to the first of these questions can be found when Junior has his life-changing conversation with Mr P, his maths teacher. When he opens up and talks about the bullying he is experiencing, Junior talks about his friendship with Rowdy and how Rowdy protects him from being bullied. However, what Mr P tells Junior is that the reason why Rowdy is so violent himself is because he is beaten by his father at home. Junior's response shows that he clearly knows this and thus Mr P's explanation is supported. Note what Junior tells the reader:
Whenever he came to school with a black eye, Rowdy made sure to give black eyes to two kids picked at random.
Rowdy is therefore shown to be a violent child, who takes the violence he receives from his father at home and allows that to transform him at school into a vindictive boy. Mr P feels that Rowdy as a character is only going to become "meaner and meaner" as he grows up. He uses this as part of his explanation why he feels Junior has to leave the reservation to avoid becoming like Rowdy and all the other Indians who have "given up" and are "defeated." It is interesting that Junior himself is unsure why he and Rowdy have become such good friends, but perhaps, given what Mr P tells Junior, it is possible to argue that Rowdy, just like Mr P, identifies in Junior something special that makes him feel protective towards him and gives him the desire to look out for him.