Complex sentence: The film was directed by Kathryn Bigelow and the screenplay was written by Mark Boal, a freelance writer who was embedded as a journalist in 2004 with a U.S. Army EOD team in Iraq.
Split into simpler sentences: The film was directed by Kathryn Bigelow and the screenplay was written by Mark Boal, a freelance writer. He was embedded as a journalist in 2004 with an U.S. Army EOD team in Iraq.