Brown was appointed coach of the Dragons for the 2003 season, becoming the youngest non-playing coach in years in the NRL at age 29. During his first season, at a match on Sunday, 13 April 2003 against Manly at WIN Stadium, a frustrated Nathan Brown berated captain Trent Barrett, Brett Firman and Lance Thompson on the sideline in the 53rd minute with the scores locked up at 12-all. Brown slapped Barrett across the cheek and grabbed the jerseys of Barrett and Thompson. The incident was seen by the crowd and other players on the big screen and proved a decisive turning point as Manly ran in five second half tries to win 38-12. After the match, Brown was apologetic to Barrett and was later fined $5,000 by the NRL.