At the beginning of Chapter 3 in To Kill a Mockingbird, why does Scout start a fight with Walter?
The answer to why they fight lies in this: Mr. Cunningham and Walter are independent people who act on their own. The importance of this fight with Walter Cunningham is shown later when Scout speaks to his father and singles him out from the mob at the jail. It is Mr. Cunningham calls off the other men and leads them away, saving Atticus from danger. And, it is Mr. Cunningham who sits on the jury and causes the others to have to debate and give consideration to Tom's innocence before returning their unjust guilty verdict.
In Chapter Two, when Miss Caroline offers Walter money for lunch, she, in effect, insults Walter, who like his father that will not accept welfare and is too proud to take her money without working for it. Scout tries unsuccessfully to explain this principle to Miss Caroline and gets in trouble for her effort:
"You're shamin' him, Miss Caroline. Walter hasn't got a quarter at home to bring you and you can't use any stovewood."
Scout tries to explain this to her teacher who is from Winston County, a county that Alabamians did not at that time consider a true part of their state. Ironically, it is this same Southern pride that Walter has that causes Scout to fight Walter because he has caused her to be scolded. Truly, she respects Walter's pride,--the battle is not over any lack of consideration for his poverty--but she is angry that he has gotten her in trouble.
The answer to this question can be found in Chapter 2. Walter Cunningham, a boy in Scout's class, is given some money to buy some lunch by their teacher. Scout thinks about telling her teacher that the Cunninghams are a large family who never have any money, but who also are too proud to suffer owing others for their charity, which is why the Cunninghams in the past repaid Scout's father, Atticus, for his legal assistance with the vegetables that they grow on the farm. But Scout realizes she cannot explain it as well as Atticus and merely says Miss Caroline "shamin'" Walter. Miss Caroline finally gets exasperated with Scout. For defending Walter Cunningham, Scout gets into trouble. This is why at the beginning of Chapter 3, Scout rubs Walter's nose in the dirt to get him back.