The New Guy (2002) on Netflix

Dizzy Harrison is an unpopular, high school geek going through a hellish senior year. In an attempt to make a new identity for himself, Dizzy gets himself expelled from his high school, learns the technics of being cool from a prison inmate, and enrolls at a new high school under the alias Gil Harris, to make new friends where he soon gains respect from the jocks and geeks alike. Dizzy then gets noticed by the head cheerleader, Danielle, and helps the school football team gain self-respect to win games. But things unknowingly begin to turn sour when Danielle's disgruntled boyfriend begins investigating into "Gil Harris'" past to uncover any dirt on him.