Arthur is Erik's sidekick and partner in crime. When Erik first arrives in town, he was going nowhere fast on the football team. He saw an opportunity to ride in on Erik's coattails, and finally make a name for himself, so he made himself useful to Erik. In the process, he becomes a thief and a murderer, and ends up handcuffed.
Mike was a good guy, and a great football player with a bright future—until his future gets a little too bright (too soon?), and he's killed by lightening.
Tino is a firecracker. He is passionate about everything he does. He is one of the stars of the Tangerine soccer team, and a friend of Paul's. He loves his teammates fiercely, idolizes his big brother Luis, and jumps into furious fistfights with anyone who makes him mad. His defining characteristic is loyalty to his friends and family, so when he finally lets Paul into his life as a friend, he really considers him a brother.
Theresa is Tino and Luis's sister, and she becomes one of Paul's friends. She is just as loyal to her family as Tino and Luis, but she's calm enough to be go-between when there's trouble between them and the outside world. She's a natural-born leader, too, whether calming her entire class down after a fight, or taking charge of her science project group. We're kind of rooting for her and Paul to get together, honestly.
Victor is the captain of the Tangerine soccer team. He's passionate about soccer and his friends, and great at motivating them to do their best. He has a habit of giving everyone a nickname, whether they want one or not, like Fisher Man, Cesar Salad, and Charlie the Tuna. Even though he loves ragging on his friends, his insults (and praises) are super smart—he calls Joey a negative integer at one point, while Cesar becomes Julius Caesar, emperor of Rome.
Antoine is the star quarterback on the Lake Windsor football team. We know he's a good guy, because he helps Luis up when he sees him get hurt by Arthur and Erik. He's actually playing for Lake Windsor illegally, because he doesn't live in that district, and eventually he 'fesses up. And he's also the first one to tell the police about Arthur killing Luis.
Antoine's little sister is as good an athlete as he is. She plays goalie on the Tangerine soccer team, but she has to keep a low profile to avoid drawing attention to her brother's illegal address. The Thomases give us another example of a family that actually helps each other out (unlike the Fishers).
Kerri is a student at Lake Windsor Middle School who has a crush on Paul. We don't know much about her—but we're definitely team Theresa.
Gino is the captain of the Lake Windsor soccer team. He's a great player, and is kind to Paul even when they're playing against each other.
Tina and Paige are Arthur and Erik's girlfriends. They don't really like they boys, but they wanted to date football players. Arthur and Erik don't really like the girls either, but they wanted to date cheerleaders. These relationships obviously have promising futures.