PURPOSE:To translate into Spanish and validate the anterior cruciate ligament-return to sport after injury (ACL-RSI) scale, and to evaluate the psychological factors that have the greatest impact on the return to play among Spanish football players. METHODS:The ACL-RSI was first translated into Spanish by two teams of bilingual experts. At the time of discharge, 114 amateur and semi-professional football players who underwent ACL reconstruction answered a questionnaire regarding demographic and injury-related data, along with the translated ACL-RSI, the Knee Injury and Osteoarthritis Outcome Score (KOOS), the Tampa Scale for Kinesiophobia (TSK-11SV) and the injury-psychological readiness to return to sport (I-PRRS). Statistical analysis included reliability tests (Cronbach's alpha and test-retest), construct validity and exploratory factor analysis. RESULTS:The ACL-RSI-Sp showed excellent internal consistency (Cronbach's α = 0.9), temporal stability (test-retest r = 0.9) and significant moderate correlations with the KOOS subscales of symptoms (r = 0.4; p < 0.01), pain (r = 0.4; p < 0.01), daily life (r = 0.4; p < 0.01), "sport" (r = 0.5; p < 0.01) and quality of life (r = 0.6; p < 0.01). Significant moderate and strong correlations were also observed for the ACL-RSI-Sp with the TSK (r = - 0.5; p < 0.01) and the I-PRRS (r = 0.8; p < 0.01), respectively. Confidence in performance (1) and fear and insecurity (2) explained 62.6% of the total variance in ACL-RSI-Sp. CONCLUSIONS:The ACL-RSI-Sp was a valid and reliable instrument to evaluate the relevant psychological factors in the return to sports of Spanish football players after ACL reconstruction. Players' confidence in performance and fear and insecurity were the most important factors influencing the return to play in this population. LEVEL OF EVIDENCE:Level IV.