Carolyn McDuffy, the California cheerleader played deliciously by Christina Ricci, will do anything for her sorority, even mentor the mentally challenged wheelchair-bound Pumpkin Romanoff (Hank Harris) in a special shot-put competition. She doesn’t expect to fall in love — she already has a jock boyfriend (Sam Ball) — but Pumpkin is so sweet and needy. Even his mom (Brenda Blethyn) is amazed at her son’s vigor, until she finds Carolyn giving Pumpkin a workout in bed. Something disquieting and boldly funny could have come out of the screenplay by Adam Larson Broder, who co-directed Pumpkin with Tony R. Abrams (it’s their debut). But after a lively start — the sorority sisters, shaken by the slightest imperfection in themselves, cannot cope with handicapped athletes — the film smooths its rough edges and reduces complex characters to sitcom stooges. Call it an opportunity missed.