Objectives: There is no consensus on the optimal treatment of young in-season athletes with anterior shoulder instability and limited data are available to guide return to play and treatment. The purpose of this study was to examine the likelihood of return to sport following an in-season shoulder instability event based on the type of instability (subluxation vs. dislocation). Additionally, injury factors and patient reported outcome scores administered at the time of injury were evaluated to assess the predictability of eventual successful return to sport and time to return sport during the competitive season following injury. Methods: Over two academic years, 45 contact intercollegiate athletes were prospectively enrolled in a multicenter observational study to assess return to play following in-season anterior glenohumeral instability. The primary outcomes of interest were the ability to return to sport and time lost from sport following an acute anterior shoulder instability event. Baseline data collection included sport played, previous instability events, direction of instability, and type of instability (subluxation or dislocation). Patient reported outcome scores specific to the shoulder were obtained at the time of injury and included the Western Ontario Shoulder Instability Index (WOSI), Single Assessment Numeric Evaluation (SANE), Simple Shoulder Test (SST), and American Shoulder and Elbow Score (ASES). All observed patients underwent a standardized accelerated rehabilitation program without shoulder immobilization, following the initial shoulder instability event. Subjects were followed during the course of their competitive season to determine return to play success and recurrent instability. Results: Thirty-three of 45 (73%) athletes returned to sport for either all or part of the season after a median 5 days lost from competition (IQR=13)(Fig 1). Of the 33 athletes returning to in-season sport following an instability event, 63% (22/33) completed the season. Athletes with a subluxation were 5.3 times more likely (OR=5.32, 95%CI: 1.00, 28.07, p=0.049) to return to sport following an initial in-season shoulder instability event when compared to those with dislocations. Logistic regression analysis suggests that the WOSI (OR=1.05; 95% CI 1.00, 1.09; p=0.037) and SST (OR=1.03, 95% CI 1.00, 1.05; p=0.044) administered after the initial instability event are predictive of ability to return to play. For every 1 point higher the WOSI scaled score at the time of injury, the athlete was 5% more likely to return to play during the same season. Time loss from sport following a shoulder instability event was inversely correlated with the WOSI (p=0.039), SST (p=0.007), and ASES (p=0.02) scores at the time of initial injury. The SST demonstrated the strongest correlation with time lost from sport, and for every 10 points higher the SST scale score was at the time of injury an athlete returned to sport 1.2 (95%CI: 0.4, 1.9) days sooner (p=0.004). Based on the logistic regression analysis, time lost from sport is predicted using the SST score after the initial instability event (Table 1). Conclusion: In the largest prospective study evaluating shoulder instability in mid-season contact athletes, we demonstrate that 73% of athletes return to play after one week. While the majority of athletes who return to sport complete the season, recurrent instability events are common regardless of whether the initial injury was a subluxation or dislocation.