Scout fought Walter Cunningham because *

Scout fought Walter Cunningham because she blamed him for being punished on the first day of school.

Explanation:

Jean Louse Finch, known under the nickname "Scout", is a young girl, and a character from Harper Lee's novel, To Kill a Mockingbird.

At the beginning of Chapter 3, it is the first day of school, and the teacher criticizes Scout's father for teaching her how to read. Scout is upset by the teacher's criticism, but the situation becomes even worse later, when the teacher offers Walter Cunningham money for lunch. Scout, aware of the financial situation of the Cunningham family, explains to the teacher that Walter never borrows money, because he cannot pay back. As a result of Scout's behavior (which the teacher considers inappropriate), Scout is punished and her hand is smacked. Scout, clearly angry and frustrated, blames Walter for her bad day, and decides to "rub his nose in the dirt."