As the episode starts, the Simpsons are at a baseball game, and Bart catches a fly ball, pushing the Springfield Isotots into the championships. The next day, Marge is shopping at a department store, but Homer is tired and can not find a place to sit, so he lies down on a mattress and ends up falling asleep. However, when he wakes up, everybody is staring at him, so he gets up and exclaims his love for the mattress and manages to sell five; he is promptly hired as a mattress salesman.

Springfield is playing Shelbyville in the championship, and is leading 5-2 in the bottom of the ninth with two outs, but Shelbyville has the bases loaded. When their batter hits the ball that could decide the game, it heads towards Bart. He drops a pop up and repeatedly fails to pick it up, allowing all four runners to walk the bases and score, giving Shelbyville the 6-5 victory. The crowd turns against Bart, who flees the stadium. When Chief Wiggum offers him a ride to safety though, Wiggum drives him back inside the stadium to allow people to throw food at him. Bart is totally humiliated and is now the town's black sheep.

At Homer's new job, he assists Apu Nahasapeemapetilon. The Lovejoys approaches him with a sex problem, so Homer sells them a new mattress called The Snugglux by Matrimonium. The Lovejoys buy it, but return it to the Simpson home next day, their problem unimproved. As Homer is writing them a refund check, the Lovejoys begin to make out on Homer and Marge's mattress, and trade their new mattress for it. That night, when Homer and Marge are unsuccessfully trying to have sex, Homer admits he traded their mattress. Also that he spent the money they kept in it on a chain originally made for Elvis (but rejected by Elvis as too tacky). The next day, Timothy and Helen Lovejoy are both singing joyfully and giggling at the Church.

Bart's humiliation goes on as Bill and Marty tell everyone on the radio, and Jimbo, Dolph, and Kearney sing a song about it called Bart Stinks. The town continues to angrily mock, chastise, and boo Bart for losing the game. Lisa tries to cheer him up by taking to see an old baseball star (Joe La Boot) who dropped a fly ball and still grew up to be rich and famous. Bart feels worse after the baseball player learns who he is and makes everybody in the building boo him. Bart starts to cry because he is hurt, much to Lisa's shock. The next morning Lisa awakes to find a deranged Bart has spray-painted "I HATE BART SIMPSON" on everything in town (including a passed-out Barney). He attempts suicide by falling off the water tower on which he has painted "I hate Bart Simpson." A shocked La Boot tries to catch him, but misses, and Bart is knocked unconscious.

While Marge is visiting him in the hospital, she hears voices chanting "Bart sucks! Bart sucks!" over and over, eventually seeing an angry mob outside. Finally fed up with all the abuse poured onto Bart, she walks out to them and angrily scold them for going too far, indicating the billboard labelling Springfield "Meanest City in America", and remarking that, more than ever, they deserved to be called that today. Feeling guilty, the entire town apologizes to Bart for hurting him and agrees to restage the game. After 78 tries (some flying into orbit, some stolen by Homer, one where Moe ran naked on the field, and even one in which the ball was disintegrated by a lightning bolt), Bart catches the ball, winning the game. Homer and Marge sneak in to the Lovejoys' home to steal back their mattress, but the Lovejoys return and excitedly rush up to bed. Reverend Lovejoy solves the problem Solomon-style – he cuts the mattress in half diagonally, this makes the matress look like a either a grilled cheese, a rueben or a chicken club sandwich. On the way Homer convinces Marge to drive behind a billboard where they have sex, just as they did on their honeymoon – complete with the same bum watching them.

Sixty years later (which the year is 2067), a 70-year old Milhouse nearly lets it slip to a 70-year old Bart that the game was faked to make up for his lack of talent. The episode ends with the ghosts of Homer and Marge watching Bart taunt Milhouse and voicing their disappointment, and Homer attempts to talk Marge in to having ghost sex with him, only for Marge to tell him that it is just not the same as when they were alive.