NOTE: This spoiler was submitted by Jeremy

The film starts with best friends PJ (Rachel Sennott) and Josie (Ayo Edebiri) getting ready to go out. They are high school seniors who are hoping to get laid before the end of the year. PJ has a crush on cheerleader Brittany (Kaia Gerber) while Josie is interested in Brittany’s fellow cheerleader Isabel (Havana Rose Liu), who is already dating their school’s star quarterback Jeff (Nicholas Galitzine).

PJ and Josie go to a carnival where most of their classmates from Rockbridge Falls High go. They run into Brittany and Isabel, where they both awkwardly fumble through their attempts to talk to them. They also run into another classmate, Hazel Callahan (Ruby Cruz), who keeps pestering them with questions and mistakenly believes that PJ and Josie went to juvie since they failed to correct her. As the girls are heading home, they see Isabel storming away from Jeff because he was checking out another woman. Josie offers Isabel a safety ride home, but Jeff begins to order her to get out of the car. PJ goads Josie into driving, and she moves up ever so slightly to bump into Jeff’s knees. He falls over in exaggerated pain while his fellow football players rush to his side dramatically. PJ and Josie drive away quickly.

As the school year starts, PJ and Josie fear for their lives because Jeff and his buddies start to antagonize them. They are called into the office of Principal Meyers (Wayne Pere) over the incident with Jeff. To get themselves out of trouble, PJ and Josie pretend that they were practicing for a self-defense club that they have started for the sake of female solidarity. Meyers buys it and dismisses them.

During their break, PJ and Josie sit with Hazel and talk about actually starting their “fight club”. While Josie isn’t so eager to go along with it, PJ tells them that if they can get Brittany and Isabel to sign up, they may have an opportunity to hook up with them. They start to go around to get other girls to join them with help from Hazel, but PJ is disappointed that they couldn’t get “hotter” girls to join. She and Josie begin by lying about being in juvie and having experience with fighting, so PJ tells Josie to punch her in the face. She does so and gives PJ a bloody nose while hurting her own hand.

PJ and Josie then go to their teacher, Mr. G (Marshawn Lynch), to be their advisor. As he is going through a messy divorce, he agrees to it. During their next meeting, Mr. G shows up, as do Brittany and Isabel, which makes PJ and Josie want to take their ruse more seriously. PJ starts by using a girl named Annie (Zamani Wilder) to fight with, but Mr. G thinks it is too much and he prepares to shut them down until Josie gives a rousing speech about how they need the club to stand together with other women, which lets him keep it going.

The club starts to get closer as they continue with their “lessons”, and some get better at fighting. At one point, they sit in a circle and discuss personal feelings and experiences, such as how almost all of them have been sexually assaulted. Josie tells a fictional account of being in juvie that inspires something in the other girls, especially Isabel.

Jeff’s best friend Tim (Miles Fowler) begins to take notice and tries to scare the girls into stopping their club. Meanwhile, Hazel’s mother (Dagmara Dominczyk) starts to notice Hazel being more active, but her daughter refuses to talk to her. One afternoon, Hazel comes home to hear her mother having sex and is horrified to discover that it’s with Jeff.

Hazel later tells PJ and Josie that she saw Jeff with her mom. Josie, who has started getting closer to Isabel, hangs out with her and tells her that Jeff is cheating on her. Later on, Hazel confronts Jeff in the cafeteria. While he tries to deny it, Hazel stepping in makes Jeff blurt out the truth. Hazel breaks up with him and then declares to the other girls in the club that she wants revenge.

The girls sneak over to Jeff’s house that night and pelt his house with eggs and throw toilet paper all over the place. Josie and Isabel start to have a heart-to-heart in their van while waiting for the other girls to be done. Hazel then plants a bomb under Jeff’s car, which goes off and destroys the car and forces the girls to flee in a panic just as Josie and Isabel are about to kiss.

The next day, the girls meet over the incident, and PJ chastises Hazel for her decision. They get into a fight where Hazel calls PJ a liar, and before she can reveal the ruse, PJ tells Hazel she has no friends and that her mom is a skank. Hazel walks away crying while the other girls, especially Josie, think PJ went too far.

Later on, Josie and Isabel hang out at home, and they end up kissing and hooking up. Meanwhile, PJ goes to Brittany’s home to help her expand her jewelry business. As they are in bed together, PJ takes the opportunity to kiss Brittany, but she gently tells PJ that she is straight.

The school then holds a pep rally where Jeff and Tim call out the fight club after they figured they were the ones who blew up his car. They get Hazel to come out and fight their toughest, most insane player, Tucker (Cameron Stout). Although Hazel gets a few good hits in, Tucker ends up overpowering her and severely injures her, forcing the girls to go to her aid. Jeff and Tim then reveal the truth about PJ and Josie to everyone, how they never went to juvie and were only doing the club to hook up with cheerleaders. The other girls’ trust in them is destroyed, and PJ and Josie end up having their own fight after Josie tells PJ she is selfish and made her go along with it, in addition to being angry that she didn’t get what she want (getting with Brittany).

After spending some time alone, Josie hangs out with a former student, Rhodes (Punkie Johnson). After giving her some advice, Rhodes informs Josie that the opposing football team, Huntington High, always gets a player from Rockbridge Falls as a victim for deadly pranks. Josie runs back to PJ and reconciles with her so that they can round up the other girls and save the football players.

PJ and Josie run to the school on the night of their big game. PJ apologizes to Hazel and gets her, plus Alice and another girl, Ella (Summer Joy Campbell), to help round up the other girls. They try to create a distraction by having Hazel plant a bomb behind a tree. It doesn’t go off, so the girls try getting the cheerleaders to make out, but when THAT doesn’t work, PJ kisses Ella long enough to distract the football players away from the field. Josie then finds a vat of pineapple juice, which Jeff is allergic to, and she realizes he is the target. The girls work together to get Jeff off the field before the Huntington players show up. When they realize what the other team plans to do, the girls, now joined by Brittany and Isabel, begin to fight the Huntington team in brutal fashion. Ella impales a guy with a sword while Brittany and PJ go after the same guy, and Josie gets Jeff off the field before the sprinklers with pineapple juice go off. He is thankful and tries to kiss her but she says no. After most of the Huntington players are knocked out or straight up dead, the sprinklers go off, but Mrs. Callahan shuts them off.

The girls are then cheered on by the rest of the school as they revel in their victory. Josie and Isabel share a passionate kiss, while PJ and Hazel may possibly be into each other. Moments later, Hazel’s bomb finally goes off.

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PJ and Josie are dorky queer high school seniors hoping to hook up with the respective cheerleader crushes, Brittany and Isabel. After an incident involving Isabel's jock boyfriend Jeff, the girls get themselves out of trouble by pretending to host a self-defense class, or "fight club", for other girls as a form of female solidarity. In reality, PJ and Josie are hoping it will get them closer to Brittany and Isabel. They even recruit their teacher, Mr. G, to be their advisor.

The girls in the group start to get closer to one another, but things start to take a turn when one of them, Hazel, catches Jeff having sex with her mom. She tells Josie, who tells Isabel, leading to her breaking up with Jeff and planning revenge. The girls egg and TP his house, but Hazel takes it a step further by planting a bomb under his car and blowing it up. During a pep rally, Jeff and his best friend Tim get their own payback by having their biggest player fight Hazel and severely injure her, and then exposing PJ and Josie's lies and real motives for the club. This causes the other girls to lose trust and respect in them, especially Isabel since she had started to develop mutual feelings for Josie. She and PJ have their own fight and split up since PJ was also upset that Brittany did not return her feelings.

Later, Josie learns from a former student that the opposing school's football team, Huntington High, always perform a deadly prank against one of the football players. Their target this year is Jeff, by planting pineapple juice (he's allergic) in the sprinklers on the football field. Josie reconciles with PJ and they round up the other girls after PJ apologizes to Hazel to get them to help. They get Jeff off the field and engage in a bloody brawl with the Huntington players alongside their own team, also joined by Brittany and Isabel. Most of the Huntington team is dead, but the school cheers on the girls for their victory, and Josie and Isabel get together, while PJ and Hazel might have something going on.