If you mean The Runner by Cynthia Voight, then Tamer refers to Tamer Shipp. Tamer is an African American student who joins the track team of which the main character, Bullet Tillerman, is a member. Bullet, who comes from an abusive family, uses running to escape from the pressures of everyday life. When Tamer joins the team, Bullet is angry that he is being asked to run with an African American student, and allows his racism to get the better of him. Tamer is a character who eventually brings out the best in Bullet, forcing him to grow up, overcome his racism, and confront his problems. In a way, Tamer is the vehicle by which Bullet learns about himself and what it means to be a man.