The details of this excerpt reveal the author’s purpose by

explaining why the fans acted like they did.
including facts and details about the topic.
encouraging the reader to believe in something.
expressing opinions about a topic.

If this is the excerpt:

Read the excerpt from It's Our World, Too!: Young People Who Are Making a Difference.

In his small Idaho school, football meant everything to Ernesto ("Neto”) Villareal, sixteen, the team’s star running back. And yet when he heard fans screaming racial insults at him and his Hispanic-American teammates, he wondered how he could keep playing for fans who felt that way. The insults also bothered Andy Percifield, a white student leader. When Neto and Andy teamed up, each using his own special power, fans began to feel heat they had never felt before.

Then, my answer is: INCLUDING FACTS AND DETAILS ABOUT THE TOPIC.