Evaluating the Chase Utley Rule: The Association Between a Rule Change and Collision-Related Injuries in Major League Baseball

Background: Major League Baseball (MLB) adopted a rule change in 2016 to reduce the number of collisions that occur when a player slides into a base. The effect of rule 6.01(j) has not been quantified, and it remains unknown if this rule change has led to improved player safety. Hypothesis: Rule 6.01(j) would be associated with a reduction in the number of collision-related injuries at second base. Study Design: Cohort study; Level of evidence, 3. Methods: Using data from the MLB Health and Injury Tracking System, we quantified the number of collision-related injuries for defensive (ie, fielding) players in the infield at the major and minor league levels between the 2010 and 2019 seasons. We compared the median number of collision-related injuries for defensive players in the infield from before (2010-2015) to after (2016-2019) the implementation of rule 6.01(j) and also calculated the difference in location of the median from the seasons before versus after the rule change. An additional 3 analyses were performed to support or contradict a conclusion that any observed reduction in injuries at the start of the 2016 season was likely caused by the adoption of rule 6.01(j). Results: The median number of collision-related injuries for defensive players at second base decreased from 58.5 to 37.5 injuries per season after the rule change, which was a 36% decrease (difference in location, 19.5 [95% CI, 5.0 to 31.0]; P = .019). In contrast, the median number of collision-related injuries at first base decreased by only 14.1%, from 49.5 before to 42.5 after the rule change (difference in location, -9.0 [95% CI, -4.0 to 18.0]; P = .16), and the median number of collision-related injuries per season at third base was unchanged at 15 per season. Conclusion: This rule change was associated with a decrease in the number of collision-related injuries, with the largest effect observed at second base, as expected.