The 1984Detroit Lions season was their 55th in the National Football League. The team failed to improve upon their previous season's output of 9–7, winning only four games. The team missed the playoffs for the first time in three seasons. In a Lions season littered with numerous key injuries, the most painful was star running back Billy Sims suffering a career-ending knee injury in a game against the Minnesota Vikings during the season. In just five seasons in the NFL, Sims would set the Lions career rushing mark at 5,106.