In To Kill a Mockingbird, what promise does Scout break that she has made to Atticus?
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.
In Chapter Nine of To Kill a Mockingbird, Scout has a troublesome encounter with Cecil Jacobs, who Scout believes has insulted her family when the boy announces publicly that "Scout Finch's daddy defended n*ggers." This does not trouble Atticus, who informs Scout that he is certain that he must defend Tom Robinson as a matter of self-respect; he knows he will not win the case, but he must pursue justice for Tom anyway because it is the right thing to do. Atticus requests that Scout keep her head high and fists down.
However, Scout ends up breaking this promise approximately three weeks later when her cousin Francis insults Atticus at the family Christmas celebration by calling him a "n*gger-lover." Scout chases him around until she eventually catches him and punches him in the mouth. While Scout does get punished by her Uncle Jack for this transgression, Jack keeps the fight secret so that Scout won't disappoint her father.