Background In 2010, Major League Baseball (MLB) and the Major League Baseball Players Association reached an agreement on an electronic medical records and injury tracking system. One goal of the system was to identify and monitor injury trends to better optimise player health and safety.

Methods Development of the surveillance system, HITS (Health and Injury Tracking System) database involved reviewing existing sports injury surveillance systems, consulting with the certified athletic trainers who record player injuries and illnesses, as well as experts who had experience with existing sports databases, and team physicians.

Results HITS includes all players from the Major and Minor Leagues rather than a sample of players from certain teams. The HITS system has a unique identifying number for each player; thus, data can be deterministically linked across various databases. Linking the data allows for investigation of injuries with regard to other key measures of exposure such as pitch count and number of hits, surgical outcomes data, personnel records to calculate cost data, and demographic data. Events included in HITS are any injury or physical complaint sustained by a player that affects or limits participation in any aspect of baseball-related activity, such as a game, practice, or warm up. Analysis of the HITS data has explored leading body parts injured during play including the hamstring, knee, shoulder, and head; select positions such as catchers; and key activities such as sliding.

Conclusions The implementation of HITS has advanced sports injury research overall and professional baseball research in particular. The richness of HITS is unprecedented and creates an opportunity to identify and monitor injury trends in baseball, and conduct epidemiologic research to better understand player risk, and optimise player health and safety through possible rules changes, equipment modifications, or medical education.