Bobby Boucher (Adam Sandler) is a 31-year-old, socially inept, stuttering, simpleton water boy living in Louisiana who rides a lawn mower to and from work, and has hidden anger issues due to constant teasing and excessive sheltering by his overbearing and domineering mother, Helen (Kathy Bates). He became the water boy for the (fictional) University of Louisiana Cougars after being told his father died of dehydration in the Sahara while serving in the Peace Corps. However, the players always torment him and the team's head coach, Red Beaulieu (Jerry Reed), eventually fires him for "disrupting" his practices. Bobby then approaches Coach Klein (Henry Winkler) of the South Central Louisiana State University Mud Dogs and asks to work as the team's waterboy. Coach Klein has been coach of SCLSU for years without success, after his brilliant playbook was stolen by Red Beaulieu.
Bobby's mother, Helen, (determined to keep him on a tight leash) tells Bobby of the evils of football and forbids him to play. Coach Klein shows Bobby his tattoo of Roy Orbison encouraging him to clandestinely go against his mothers' wishes. After being picked on again by his new team, Coach Klein encourages Bobby to strike back, which leads to him knocking out the team's quarterback. Coach Klein convinces Bobby to enroll as a student at SCLSU and play for the team, which he agrees to do as long as nobody tells his mother.
Bobby quickly becomes one of the most feared linebackers in college football, hitting opposing players with injury causing force. The Mud Dogs manage a winning streak and earn a trip to the annual Bourbon Bowl to face the Cougars and Coach Beaulieu. Bobby's newfound fame also allows him to rekindle a relationship with his childhood friend and high school crush Vicki Vallencourt (Fairuza Balk), a local Goth Girl mechanic and "football groupie" who has been in prison multiple times. However, after Bobby invites Vicki to his trailer where he introduces her to his mother at a cookout, Helen forbids Bobby from seeing her again.
Coach Beaulieu reveals that Bobby never finished high school, making him ineligible for college and football. However, Bobby manages to pass his GED exam, despite his mother's objections about him going back to college. She then fakes falling ill to keep Bobby from playing, but eventually relents after witnessing the town residents' support for Bobby. The next day, Helen tells Bobby the truth what really happened to his father and why she was faking her illness. Helen explains that Bobby's father changed his name to Roberto and left Helen for a voodoo priestess, while she was pregnant. This damaged Helen so bad that it led her to execessively sheltering Bobby all his life from the outside world. She was afraid Bobby was going to leave her too when he became old enough and tried to keep him all to herself by hiding him from everyone else who depended on him. Helen realises the best thing for her to do is let him go since he's made a lot of wonderful friends and encourages him to play in the Bourbon Bowl.
Arriving at halftime of the Bourbon Bowl with Helen and Vicki, Bobby manages to encourage the losing Mud Dogs to make a comeback. The team admits that he has become their heart and soul of the Mud Dogs. Seeing the overwhelming support at the Bourbon Bowl, Helen changes her mind about football being for the devil. With Bobby's help, Coach Klein overcomes his fear of Red Beaulieu by imagining him as something he's not afraid of(i.e. a baby and a cocker spaniel). This helps Klein create spectacular new plays that allow the Mud Dogs to catch up. Helen helps the cheerleaders out by making coffee and it helps keep their energy up as they cheer their fans on to rally, while Vicki is seen giving out water to the Mud Dogs. During the final play, Bobby throws a touchdown pass and the Mud Dogs win the Bourbon Bowl. Bobby is named the MVP of the game.
Sometime later, Bobby and Vicki get married and are heading to the riding lawn mower. Although Helen still has some reservation on Vicki, she admits he's got a fine woman who'll take care of him. On their way out Bobby's father, Roberto, makes an unexpected appearance, telling him that he heard from ESPN that he may go to the NFL. Bobby tells him that he's not going to the NFL because he likes to stay in school and graduate. Roberto tries to convince Bobby to leave school and go to the NFL, hoping to personally profit as his father. However, an enraged Helen charges in and tackles him down causing cheers from the attendants. Bobby and Vicki leave to consumate their marriage.