That was autobiographical and based on a book. Not created for or run by Denzel. He got a production credit and lead acting role.
People wouldn't have gone to see it if Denzel wasn't in it though..from the wiki for the movie....
The film marks the directorial debut of Denzel Washington, the first screenwriting credit for Antwone Fisher, and the first feature film-role for Derek Luke.
Washington was brought the script originally just to play the part of Jerome Davenport. But Washington’s agent called Black and told him he not only wanted to act in the film, he wanted it to be his directorial debut.
Fisher had known Luke as a young actor working at the Sony Pictures gift shop while he was writing the screenplay. Fisher encouraged Luke to try out for the part. An audition with casting director Robi Reed-Humes went well enough that Luke was called in to meet with Washington.
[4] Washington was impressed with Luke’s audition and asked that he personally deliver the good news.
Washington (aware that he was working with an unknown) stated that he wanted to give a younger generation of black actors their chance to come alive on-screen. To prepare the cast, Washington required each actor to know his/her character's history and story inside out before coming to the set. This mandate included everyone from Luke in the title role to key cast members like Vernée Watson Johnson, who plays Fisher's long-lost Aunt Annette, Novella Nelson in the role of Fisher's foster mother, Mrs. Tate, Viola Davis as Fisher's mother, newcomer De'Angelo K. Wilson, seen opposite rapper
Eminem in
8 Mile, as the grown-up Jesse, Malcolm David Kelley as the young Antwone, and Corey Hodges as the teenage Antwone. Washington repeatedly told the cast and crew “We’re doing it for Antwone.”