PurposeTo identify prognostic factors associated with a delayed return to sport (RTS) time in amateur athletes who return to full participation after a primary isolated anterior cruciate ligament (ACL) reconstruction. MethodsA retrospective review was performed among athletes who underwent ACL reconstruction between October 2014 and October 2021. Inclusion criteria were any amateur athletes with an ACL reconstruction that had a documented RTS and greater than one-year follow-up. Non-athletes, multiligamentous knee injury, and missing documented RTS timelines were exclusion criteria. RTS was defined as participation in athletics at a level equivalent to or higher than the pre-injury level participation. Demographic and prognostic factors, including prior knee surgery, meniscal involvement, level of participation, surgical approach, and graft type, were recorded along with RTS time and analyzed via Poisson regression. Results91 athletes, average age 18.8 (± 6.7) years, who underwent ACL reconstruction at a single institution from 2014 to 2021 were identified with an average follow-up time of 4.6 (±2.5) years [range 1.1, 9.0]. Meniscal involvement [1.11 (95% CI: 1.08, 1.15), p < 0.001] and previous knee surgery [1.43 (95% CI: 1.29, 1.58), p < 0.001] were related to a delayed RTS. Quadriceps tendon and bone-patellar tendon-bone (BTB) autografts, as well as allograft showed a significant association with a longer RTS time when compared to hamstring autograft [1.16 (95% CI: 1.13, 1.20), p < 0.001; 1.04 (95% CI: 1.01, 1.07), p = 0.020; 1.11 (95% CI: 1.03, 1.19), p=0.004, respectively], as did anteromedial portal drilling, when compared to the outside in approach for femoral drilling [1.19 (95% CI: 1.16, 1.23), p < 0.001]. ConclusionPrior knee surgery, anteromedial femoral drilling, quadriceps tendon autograft, and meniscus tear were most associated with a delayed timeline for RTS among young athletes who were able to return.