When Lori and Leni buy identical dresses from the mall, a fight breaks out in the Loud House, and the Sister Fight Protocol is initiated.
Lincoln enters the living room, and is surprised to see that it is empty. He then walks towards the kitchen, only to find Luna guarding the entrance. She tells him that Lori is in the kitchen cooling off after a fight she had with Leni, and won't let him in. Lincoln insists on going in, as he's hungry, but Lisa tells him that she found something under the sofa cushions. She hands him a bagel, but as Lincoln takes a bite of it, she informs him that it is covered in lint, dog hair, and a booger. He runs upstairs, only to find Lana guarding the bathroom. She tells him that Leni is in the bathroom cooling off, and that he can use a bucket to throw up in, which he reluctantly agrees to. Later on, he wants to watch a Monster Truck Rally on TV, but Lynn, Lucy, and Lola won't let him, as it would only provoke Lori and Leni. Lincoln asks what their fight is about, and they finally tell him that they both bought the same dress, and are angry at each other for it. Lincoln is flabbergasted at the two of them fighting over such a petty thing, but his sisters tell him that it's a sister thing, for which they have a sister protocol, and that he should stay out of it.
Lincoln can no longer stand what Lori and Leni's fighting is causing, so he decides to try and help them make peace. He goes into their room, only for them to be sitting there perfectly fine, and they both try to tell him that he doesn't need to try and help them resolve it, as it's been resolved. Unfortunately, he doesn't listen, and causes them to fight again when he reveals what they both say about each other behind their backs. This makes Lori and Leni even angrier at each other, and that makes the fight get even worse. Lisa pulls out her threat level chart for fights, and they walk off, and tell Lincoln to let them handle it. Later on, Lincoln's room is being used to allow either Lori or Leni to temporarily house them, while the other passes by the upstairs hall. At dinner time it only gets worse, when they have to dine with Lori and Leni separately, so that neither of them thinks the family is siding with one or the other. Things get even worse when Lincoln's bed sheets and blanket are gone, so that they can be used as a divider in between Lori and Leni. Lincoln tries to help settle this again, which only worries the other sisters, and they try to tell him to just allow sister fight protocol to settle this. He suggests to forget sister fight protocol, and insists that Leni sleep in Luna and Luan's room, while Luna sleeps in Lori and Leni's room for the night. They agree to this, but the other sisters suggest that it's a terrible idea, and even Lily chastises him for it. However, Lincoln insists that this will be sorted out in the morning.
The following morning, Lincoln awakens to thinking that everything is back to normal, only to hear Luna and Luan fighting. They both argue over whether it was Lori or Leni who had the right to be mad at the other, and it leads to them insulting each other. Now sister fight protocol has to be used to separate the two of them, and once again Lincoln's room is used as a spot to temporarily house one of them. Lisa tells Lincoln that the fight has escalated even worse on her chart, and this causes Lynn Sr. to panic, as he and Rita lock themselves in their room with Lily. They continue with their protocol of keeping the fighting siblings separate from each other, but when Lola and Lana accidentally cross paths with Luna and Luan, this causes them to start fighting as well. Bobby comes by to deliver pizzas to the family, but he delivers one to their parents through their bedroom window, and they advise him to leave the rest on the porch, and run off, as soon as he rings the doorbell.
Later on, Lynn is eating pizza, while Lucy chastises her for slacking on the job, and this leads to the two of them also getting into an argument. Lisa is now frightened, as the chart is at the highest level of disaster, and Lana angrily bites into it, which causes Lisa to start fighting as well. At this point, every one of the sisters are arguing, and Lincoln is now unsure about what to do, so he decides to flee the house for the rest of the day.
Later on, Lincoln is at Clyde'shouse explaining his dilemma, and Clyde is listening to him, as if he were a therapist. Lincoln explains that the sister fight protocol is ridiculous, and only makes everything worse, and says that if they allowed him to help, he would resolve things. The following morning, he returns home to try and fix the problem, but everything is quiet. He opens the front door to find his sisters sitting peacefully in the living room, and they explain that they resolved everything themselves, thanks to him leaving, since he wasn't there to butt in. They explain that their sister fight protocol works, and that he shouldn't butt in. He finally agrees to this, but, unfortunately, thanks to his honest truth, he reveals more things that the sisters say behind each other's backs, and they start to fight once again. When Lynn Sr. comes out of his bedroom, thinking it's over, every one of the sisters begin fighting again, and this time, Lincoln hides with his parents in their bedroom, to avoid the sisters' brutality.
"Study Muffin": There is a real eye flying out of the fight cloud when the sisters start fighting.
Three details about the Loud sisters are revealed in this episode:
Leni's skin can't tan.
Lynn can't stand Lisa's spitting when she speaks.
Lana farts in her sleep loud enough to block off Lola's snoring.
Lincoln mentions that Lola snores as loud as Pop-Pop, which could be a reference to "Making the Case", where Lincoln's footage of Lola shows that she sleeps rather noisily.
Lincoln mentions Leni saying Lori looks like Aunt Ruth in that color of dress, then says "...and who wants that", even after portraying Aunt Ruth in "Suite and Sour".
Every Loud sister gets in a fight with their roommate, except Lisa who got in a fight with Lana instead of Lily. In addition, Lily is the only sister who was not involved in any fights, except for the ending.
A storyboard image featuring Luan getting angry at Lincoln from this episode was present long before it even aired, even before this episode was announced.
All the fights of the sisters and the reasons why they fight:
Lori and Leni: Bought the same dress.
Luna and Luan: How Lori and Leni got the dress.
Lana and Lola (1/2): Stepping into each other's zones.
Lynn and Lucy: The former eating pizza.
Lana and Lisa: The former destroys the latter's chart.
Everybody (1/2): They argue and attack each other.
Lynn and Lisa: Lincoln's secret of Lynn saying she needs a windshield wiper every time Lisa talks.
Lana and Lola (2/2): Lincoln's secret of Lana saying Lola snores likes Pop-Pop.
Everybody (2/2): Lincoln's big mouth.
In the Latin American dub of the episode, Lucy's line "Gasp" is replaced.
Everybody was informed about the sister fighting protocol, even Lily (the baby) and Bobby (non-Loud) but not Lincoln (the only boy).
The Sister Fight Protocol is sexist, since the sisters told Lincoln he wouldn't understand, due to the protocol being "a sister thing" (hence why they never informed him about it in the first place).
Brawl in the Family - The title of this episode is a parody of the ever so controversial 1970's sitcom All in the Family.
The Simpsons - There is an episode of the show with the same title as this episode.
United States Armed Forces - "DEFCON" stands for "defense readiness condition", and is an alert state used by the United States Armed Forces. A "DEFCON 5" is actually the lowest state of readiness. The DEFCON system, in reality, counts down, as it gets more dangerous; this situation would actually be classified as DEFCON 1 which is the highest defense code in the United States.
Eau de Death - When Lucy told Lynn she smelled like crusty athletic socks she responded with saying "oh, like Eau de Death is better" which references the scientifically made cologne of the same name that is meant to make you smell like the undead.
Back to the Future Part II - The sports almanac Lynn is reading "by Biff" resembles the one from the movie, which is stolen by a bully named Biff Tannen, so he can travel back in time, and get rich by betting on sporting events he already knows the outcome of.
Lana had some toilet paper stuck to her foot while she was talking to Lincoln about his bedsheets. Later, when Lana was waking up the others, the toilet paper was missing.
It is revealed that there's a sister fight protocol when two sisters get into a fight. However, no such protocol is featured in the episode when a similar incident happened when Lynn and Lucy fight with each other during the events of "Space Invader".
That could mean "Space Invader" take place after this episode.
When Lori and Leni start arguing after Lincoln's first attempt to end their fight, their lip movements do not match what they're saying.
At the end of the episode, Lincoln triggered Lisa and Lola into arguing, so it doesn't make sense why the remaining sisters began arguing.
In that same scene, Lisa was arguing with Lynn, but when the remaining sisters were seen arguing, Lisa was seen arguing with Luna, while Lynn was arguing with Luan.
When Lynn, Lucy, and Lola attack Lincoln to prevent him from grabbing the TV remote, Lana's cap can be seen in the smoke cloud, despite Lana not being present.
When Lincoln is about to enter the house near the end of the episode, he has a trash can lid for a shield, but when he opens the door, he doesn't have it anymore. It could be possible that he put it aside after coming in.
At the dinner scene, when the family is switching their mostly eaten plates of spaghetti for some fresh new plates, Lynn Sr. has a tray under his plate. However, the tray is not seen in other shots of said scene.
Lynn's eyelashes are missing when Lisa spits in her face.
When Lori was arguing with Leni about Lincoln saying that she said she looks like Aunt Ruth, her eyelashes were missing.
When Lincoln notices his bedspread missing, he mentions both his sheets and blanket, but when he takes them back, only his blanket can be seen.
When Lincoln leaves Lori and Leni's room in the beginning of the episode, the stairs were missing.
In the Italian dub, Lincoln's line when he sees that his sisters are not fighting anymore ("What's going on? What happened to the fighting?") is missing the "to the fighting" part, leaving a brief scene where his mouth is moving but nothing comes out.
Constant mentions of the "Sister Fight Protocol".
The Loud sisters bickering.
The sisters telling Lincoln to butt out whenever the protocol occurs.
Everyone (including the parents) staying out of the brawl.
Lincoln's room being used for a Loud sister.
Characters mentioning about the dress.
Lincoln trying to fix their problems, only for things to get worse.