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The response time (RT) in the sprint start in athletics is determined automatically from sensors on the blocks but the final decision on whether an athlete is disqualified is determined by visual inspection of the sensor data. This study explored the level of uncertainty of the visual detection of athletes’ RT in the sprint start. Fifteen sprinters performed six sprint starts while forces from the front block, rear block and hands were recorded. Two experimenters performed visual RT detection on two consecutive occasions using two sizes for the analysis window. Intra- and inter-reliability analysis indicated that the mean level of uncertainty of the visual detection was approximately 20 ms for the starting block data. More research is needed to formally assess the precision of the visual detection, which may result in changes in the current false start regulation.