Melinda Sordino, the protagonist of Laurie Halse Anderson's Speak, is not liked by her new schoolmates at Merryweather High School. Prior to her freshman year, Melinda had a close circle of friends. During the summer before her freshman year, Melinda and some of her friends went to a party. It was this party which changed Melinda's life.
At the party, Melinda was raped by Andy. Scared, Melinda calls the police. The police then come to the party and break it up, arresting a few of the attendees.
The pep assembly is the first time where many of her classmates realize who she is: the girl who called the cops. One girl's brother, the girl who pulled her hair and kneed her in the back, got into a lot of trouble. The girl, angry at Melinda for causing her brother to get into so much trouble, decided the best way to warn Melinda that she did not like her was to act out physically against her.
It is the beginning of her freshman year of high school, and Melinda is not liked by her schoolmates. Before school started, Melinda attended a party and called the cops. This made her disliked by all the people who attended the party. The girl who was yanking her hair obviously does not like her and the reason is the same as all the others who do not like her.