Lee creates sympathy for Scout because she is facing a world that is unfair in ways she does not understand.
We feel sorry for Scout from the very beginning of chapter 9, when she is fighting Cecil Jacobs for saying “Scout Finch's daddy defended niggers.” She has no idea what he is talking about, but she knows it’s bad because of the way he said it so she decides to fight him. When she asks Jem and her father about the incident, she does not really get much clarity.
Atticus sighed. "I'm simply defending a Negro- his name's Tom Robinson. He lives in that little settlement beyond the town dump. He's a member of Calpurnia's church, and Cal knows his family well. (ch 9)
Later, things only get worse for Scout when she goes to the family plantation, Finches’ Landing, for Christmas. There, her uncle spanks her for getting in a fight with her obnoxious cousin Francis, and does not listen to her side of the story.
What really happened was that Francis explained how his grandmother, Scout’s Aunt Alexandra, said Atticus was a disgrace to the whole family.
"Just what I said. Grandma says it's bad enough he lets you all run wild, but now he's turned out a nigger-lover we'll never be able to walk the streets of Maycomb agin. He's ruinin' the family, that's what he's doin'." (ch 9)
Scout is getting more and more frustrated. Everyone is calling her father names and he says he is doing nothing wrong. She does not understand racism. It makes no sense to her that her father is being ostracized by the town (and apparently the family) for defending a black man accused of raping a white woman.
Jack apologizes for spanking her without listening to her, and Atticus makes sure she overhears a conversation in which he explains to Jack why he took the case. Still, Scout has a long way to go before she fully understands what is going on.
Every reader remembers finding out that the world was not fair. Scout is young, and we feel her little injustices deeply. We understand that she is caught up in an adult problem that still immediately affects her, and she has no hope of understanding it until she grows up fast.