The COVID-19 pandemic led to the discontinuation of soccer activities at all levels of play. Injuries to the anterior cruciate ligament (ACL) are still one of the most severe injuries in soccer. The aim of this investigation was to analyze the changes in the incidence and mechanism of ACL injuries in professional and amateur soccer before and after the lockdown period. Injury data were prospectively collected using the database ‘ACL registry in German soccer’. Between 2019 and 2021, 10 matches in professional, semi-professional, and amateur leagues before and after the lockdown were analyzed for the incidence and mechanism of ACL injuries. Data were collected using standardized and recently published study methods. Mean incidence of the 84 ACL injuries recorded during the study period was 0.083 injuries per 1000 h of exposure before and 0.079 injuries per 1000 h of exposure after the lockdown period (p = 0.699). In amateur soccer, the incidence of ACL injuries increased significantly from 0.058 injuries per 1000 h of exposure before to 0.128 injuries per 1000 h of exposure after the lockdown period (p = 0.026), in contrast to professional (p = 0.436) and semi-professional (p = 0.802) soccer. The predominant mechanisms of ACL injuries were non-contact injuries (pre-COVID: 59.1%; post-COVID: 57.7%) and indirect contact injuries (pre-COVID: 31.8%; post-COVID: 30.8%). The absence from training and match practice in German soccer during the COVID-19 lockdown led to a significantly increased ACL injury rate in amateur leagues, while in professional and semi-professional soccer no differences were reported. The mechanism of ACL injuries did not change after the lockdown period.