Viola Hastings (AMANDA BYNES) is a star player on the girls' soccer team at Cornwall Academy. When that sports program is cut, however, the boys soccer coach won't let her play on his team, and her boyfriend -- the captain of the team -- Justin (ROBERT HOFFMAN) won't attest to her skills. Since she doesn't want to be a debutante like her mother Daphne (JULIE HAGERTY) desires, Viola needs a plan, and it arrives in the form of her twin brother Sebastian (JAMES KIRK).
With him wanting Viola to cover his absence as he travels to play his music in London, Viola comes up with an idea. With the aide of makeup artist Paul (JONATHAN SADOWSKI), Viola transforms herself into Sebastian and then heads off for Illyria Prep where her brother was set to attend before his impromptu departure. While posing as him, she'll try out for the soccer team led by Coach Dinklage (VINNIE JONES).
But first, she must fool her roommate Duke (CHANNING TATUM) and his fellow soccer buddies, including Andrew (CLIFTON MURRAY) and Toby (BRANDON JAY McLAREN), that he's really a guy. "His" odd demeanor initially confuses and repels them, but a bit of romantic subterfuge quickly convinces them that he's a true ladies man and it's not long before the lovely Olivia (LAURA RAMSEY) is attracted to "Sebastian."
The problem, however, is that Duke likes Olivia, and thus Viola tries to get her to like him. That is, until Viola starts to fall for Duke, all while having to deal with Sebastian's pushy girlfriend Monique (ALEX BRECKENRIDGE), geeky nerd Eunice (EMILY PERKINS) who falls for Viola's Sebastian, and both Headmaster Horatio Gold (DAVID CROSS) and preppy snitch Malcolm (JAMES SNYDER) who separately and then collectively question "Sebastian's" gender.
As she tries to juggle all of the romantic longings, and maintain her ruse as her brother, Viola attempts to make the squad and then compete against the Cornwall team to prove her abilities on the field.