Background: There is a paucity of literature regarding injury incidence, mechanism, and return to play in National Football League (NFL) players who have sustained traumatic posterior hip instability. Purpose: To describe the incidence of traumatic posterior hip instability and the rate of return to play in NFL players across 18 seasons. Study Design: Descriptive epidemiology study. Methods: We retrospectively assessed all traumatic posterior hip dislocations/subluxations that occurred during football-related activities in the NFL seasons from 2000 through 2017. Player demographics and injury data (injury mechanism, season of injury, treatment, days missed, and return to play time) were collected from all 32 NFL teams prospectively through a leaguewide electronic health record system. Descriptive statistics are presented. Results: Across the 18 NFL seasons, 16 posterior hip instability injuries in 14 players were reported, with a maximum incidence of 4 (25%) in 2013. Posterior hip instability was predominantly sustained by offensive players (64.3%), with tight ends being the most affected (31.3%). Half of the injuries occurred during the regular season, 43.8% in the preseason, and 6.2% in the offseason. Of all injuries, 37.5% were noncontact, while 56.3% involved contact (direct or indirect), and 6.2% were of unknown mechanism. Among noncontact injuries, 66.7% occurred during cutting and change of direction while sprinting. The time of return to full participation was documented for 11 of the 16 reported injuries (68.8%); among them, the mean time loss was 136.7 ± 83.8 days—143.3 ± 99.6 days if the player underwent surgery (n = 4) and 116.7 ± 76.2 days missed by players without surgery (n = 6)—the treatment modality was unknown in 1 player. Conclusion: Although the incidence of traumatic posterior hip instability during the study period was low, all injured athletes missed time from football activities and competitions. Injuries that required surgery led to more missed time than those that did not. Ongoing research to understand risk factors and mechanisms of this injury, in conjunction with improvements to prevention and rehabilitation protocols, is necessary to ensure the safety of professional American football players.