Lisa is failing gym. To make up the grade, she joins a pee-wee hockey league. Soon, her team must face off against Bart's, putting them in direct competition.
Due to impossibly low test scores, Principal Skinner starts to give out academic alerts so the children's parents can know they're doing poorly. After a series of kids receive their alerts, Lisa is called up, shocking everyone. It is then revealed that she is failing gym. Lisa, terrified, goes to her PE teacher and is told to join a Pee-Wee team outside of school. After a sequence of failed attempts at sports, Lisa finally joins a hockey team sponsored by Apu—which just happens to be Bart's rival team. Having talent in Hockey similar to Bart's own, she helps turn his team around and Homer starts paying more attention to Lisa. Bart is not happy about the lack of attention and more so when Marge tries to hang out with him.
After Lisa excels at both sports and school, Bart thinks he must become a scholar. This doesn't work out, as he been a slacker in school for his whole life. After class, Nelson and his friends confront Bart and prepare to beat him up for wasting Mrs. Krabappel's time. He is inadvertently saved by Lisa who scares off the bullies and instead of being grateful, he accuses her for stealing Homer's affections away from him. This leads to a rivalry between the entire family, which Marge is less then pleased about, having tried to keep the peace with them and arouses Homer.
When Lisa and Bart play each other, Marge berates Homer for his behavior. He tries to defend himself, but she isn't in the mood and thinks he's a selfish father for starting the whole rivalry. Homer tries to get her to choose a side, but Marge asserts herself and tells him that she loves all three of their children regardless. She tells him that when they get home, Homer is going to be sleeping in the couch. The game gets down to the wire, with the stadium split between Bart fans and Lisa fans, while Marge is the only one maintaining neutrality. However, when Bart is chosen to take the penalty shot against Lisa, the goalie, they both reminisce about how they helped each other as younger kids (Lisa giving Bart a bandage after he falls off his bike, Bart giving Lisa one of his scoops of ice cream when her own falls on the ground). Lisa and Bart throw their hockey gear on the ice and hug. Homer then remarks that they are both losers and the stadium erupts into a riot. Marge is proud of Bart and Lisa, while a despondent Homer turns his attention towards Maggie.