In his first directing gig, adapting the 2003 young-adult coming-of-age novel by K.L. Going, actor Matthew Lillard (Scream, The Descendants) does a nice job. He’s got a generous touch with the performers (led by Jacob Wysocki, the chubby star of Terri), whom he sends hurtling around various Seattle locations. Fat Kid is partly about the formation of a rock band, and Lillard gives the movie plenty of punk energy. (Pearl Jam’s Mike McCready supplies the score.) Teenagers will surely relate to 17-year-old Troy, an underconfident outsider who lives with a gruff but loving single father (Billy Campbell) and younger brother. Into his miserable life comes Marcus (the hyperactive but endearing Matt O’Leary), a teen street addict who challenges Troy to form a band with him. Fat Kid is a straightforward, peppy, pleasing movie that’s been updated just enough for the age of Facebook. (Troy vomiting onstage becomes a YouTube viral sensation and great publicity for the band.) Adults will find Going’s story too simple, of course, which is why we call them young-adult books. But the simplicity works. If Marcus can say, “Don’t disappoint me, Troy,” you can be sure he won’t.