Scout breaks her promise to her father, Atticus Finch, that she will not fight.
Chapter 9 opens with Scout threatening Cecil Jacobs, who made an announcement in the schoolyard that Mr. Finch defended n*****s. But, Atticus cautions Scout, telling her that he has to defend Tom Robinson. Later on, when Cecile Jacobs, imitating his father, questions the integrity of Atticus, Scout is ready to fight, but she stops herself lest she "let Atticus down."
However, not long after the encounter with Cecile Jacobs, it is the Christmas season and Jem and Scout travel to the home of Aunt Alexandra, where they discover that their cousin Francis has adopted the same attitude about Atticus as Cecile. After Francis shouts an invective about their father similar to the one uttered by Cecile, "this time [Scout]splits her knuckles on his front teeth...and sailed in with [her] right [hand]...."
For this action, Scout is punished by Uncle Jack, but he fails to listen to Scout's side first. After she tells her uncle what Francis said to her, Jack is furious and vows to punish him. But, Scout begs him not to say anything because she has promised her father not to fight;Jack promises, and he only mentions to his brother Scout's use of inappropriate words.