The Big Bang Theory Season 1 Episode 13 : The Bat Jar Conjecture
The guys decide to compete in a physics bowl after finding out that strong competitors have dropped out. However, they find Sheldon's showboating too much and kick him off the team. Upset, Sheldon vows to form his own team and compete against them. The guys, in need of a fourth member, ask Leslie Winkle to join them; she rejects the offer at first, but reconsiders after finding out they are going against Sheldon, who has often criticized her research.