Scout thinks Uncle Jack treated her unfairly because he punished her without listening to her side of the story.
At Christmastime, Scout is going through a phase. She uses bad language, and Uncle Jack does not like it. Atticus says she will grow out of it and basically ignores it.
Scout’s annoying cousin Francis pushes several buttons, trying to find one to rile Scout. He finally succeeds when he insults her father, and she attacks. She calls Francis a “whore-lady” (even though she has no idea what it means), and he tells on her. Uncle Jack spanks her, and is surprised when she is upset.
When Uncle Jack asks her why she is upset, she explains.
"Well, in the first place you never stopped to gimme a chance to tell you my side of it- you just lit right into me. … an' in the second place you told me never to use words like that except in ex-extreme provocation… (ch 9)
Scout explains that she was provoked, and Jack should have listened to both sides. Jack concludes that he will never understand children, and asks Atticus about it.
This incident foreshadows the unfairness Scout will encounter with Tom Robinson’s trial. Just as Jack punished Scout without getting the facts, the jury convicts Tom unfairly.
When Uncle Jack visits for Christmas, he tells Scout not to use any bad words "unless there's extreme provocation connected with 'em" (meaning she shouldn't curse unless she has very good cause). Scout gets into a fight with Francis, Aunt Alexandra's know-it-all grandson, who calls Atticus a "nigger-lover." When Francis continues to mock Scout, she hits him and swears at him and gets in trouble with Uncle Jack, who has commanded her to act more ladylike.
Scout feels that Uncle Jack is unfair in part because he hasn't listened to her side of the story, as Atticus always does. In addition, Scout thinks Uncle Jack is unfair because he hasn't heard what Francis called Atticus. Scout says, "I swear before God if I’ll sit there and let him say somethin' about Atticus." She is loyal and wants to defend Atticus. Uncle Jack realizes that Scout was justified in being angry at Francis and vows to tell Aunt Alexandra what happened. He also bandages up her hand.