The men of Springfield become obsessed with a violent new string of mixed martial arts (MMA) competitions called "Ultimate Punch Kick and Choke Championships" (UPKCC). Bart begins to fight in small MMA matches of his own at the playground of Springfield Elementary School. While he and Nelson are fighting in one match, Marge sees him and is disgusted by the violent nature of the entire sport. She and a group of concerned women begin protesting the sport in front of the MMA stadium. Marge decides to go on stage before a match begins and demands that everyone cease the sport entirely. Chett Englebrit, creator of the sport, agrees with Marge but only if she can fight him and win.
Marge begins to train for the event, practicing rhythmic gymnastics. However, the family believes that her methods are unsuitable for the extreme task at hand and get her professional help. She learns boxing from Dredrick Tatum, wrestling from former Yale wrestler Mr. Burns, jujitsu and Judo from Akira, and bullying from Jimbo, Dolph and Kearney. Now fully trained, she enters the ring (after the announcer introduces her as one of his "Moms I'd Like to Fight") with Englebrit and is immediately knocked to the ground. Bart wants to stand up for his mother and runs into the stadium to take her place, but is thoroughly thrashed by Englebrit. Marge witnesses this and effectively beats Englebrit, winning their bet. Marge pulls down the ring's microphone and begins to give a speech about the demise of the violent sport. She realizes, however, that everyone has already left the building to watch a drunken brawl in the parking lot.
Bart and his sister, Lisa, enter the empty ring and decide to settle their lifelong feud then and there. As they approach each other to throw a punch, the credits begin, but the scene immediately returns to depict Lisa easily punching Bart to the ground.