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"dalek" writes:

I've written previously about how Statcast data is changing professional baseball [soylentnews.org], but the application of the data has caused at least one very adverse effect: being a pitcher in today's game is bad for your health.

Two of the ways to be an effective pitcher are to generate a lot of swings and misses, and to induce a lot of poor contact. Poor contact means balls that are hit with low exit velocities, or at very high or low launch angles, and these disproportionately result in outs. Statcast data shows that pitchers can achieve this by throwing at high velocities [fangraphs.com] and with a lot of vertical or lateral movement on their pitches [fangraphs.com]. The pitch movement is achieved by spinning the ball at a high rotation rate, and the Magnus effect [wikipedia.org] creates a pressure gradient force across the baseball that deflects it away from its original trajectory. Fastballs tend to have backspin, which imparts an upward acceleration. However, curveballs spin forward and have a downward acceleration, and it's also possible to generate lateral movement. The direction and amount of movement on a pitch is also sometimes referred to as its shape.

The desire for higher velocity and spin rates has led to the rise of "pitching labs" that develop training programs that are very effective at increasing arm strength, improving pitching mechanics, and raising the spin rate of pitches. This comes at a price, however, which is more stress on a pitcher's arm. Major League Baseball (MLB) teams have tried to account for this by allowing pitchers to throw fewer pitches per game and giving them more rest between outings. The added rest helps pitchers consistently throw with high velocity and spin rates, at least for awhile. But all of this added stress seems to have a cumulative effect on a pitcher's elbow. The weakest point is often the Ulnar collateral ligament (UCL), and a partially or completely torn UCL has become an increasingly common pitching injury.

Prior to the increased focus on pitch velocity and shape, high pitch counts were generally considered the biggest factor in UCL injuries. However, the data show an upward trend in fastball velocity in recent years corresponding with a large increase in elbow injuries [si.com]. As this YouTube video from WIRED [youtube.com] shows, throwing a fastball at the hardest velocities seen in MLB places an incredible amount of strain on a pitcher's elbow to the point that it exceeds what the UCL can withstand. Small tears form in the UCL from the forces needed to throw a pitch that hard, and the long-term effect of continuing to pitch under these conditions is often a ruptured ligament.

Several decades ago, a torn UCL was generally a career ending injury. In 1974, Dodgers' pitcher Tommy John [wikipedia.org] was the first baseball player to undergo a UCL reconstruction [wikipedia.org], which involves grafting a tendon in place of the UCL, taking the tendon from elsewhere in the body or a donor. The procedure has become known as "Tommy John surgery" and has a high success rate, though with a long recovery time. However, continuing to pitch with high velocity and spin rates has led to the injury recurring a few years later and requiring a second surgery. There is also evidence that spin rates place a high level of stress on the elbow and are also correlated with arm injuries [fangraphs.com]. MLB also imposes a pitch clock, limiting the amount of time a pitcher can rest between pitches. Although the pitch clock improves the pace of games, it has also been cited as a potential injury risk [cbssports.com].

The obvious question is why pitchers would be willing to throw pitches at high velocities and spin rates knowing that the result is likely Tommy John surgery. The answer is that there are only so many spots on a major league roster available, and if one pitcher isn't willing to assume that risk, someone else will. The best starting pitchers get massive contracts that pay tens of millions of dollars per year, so there's a lot of money potentially available for those willing to accept the high risk of injuries. Even at lower levels, pitchers know that if they want to be successful, they need to be able to throw the ball hard. There has even been a large increase in youth pitchers having UCL injuries and undergoing Tommy John surgery [nbc26.com]. Some MLB pitchers like Josh Hader [espn.com] and Garrett Crochet [nytimes.com] have tried to impose their own limits on how teams can use them, a move that has been somewhat controversial [nytimes.com].

Fortunately, the same data that allows us to link pitch velocity and spin rate with effectiveness may also offer a solution to reduce injuries. Tracking pitch velocity and spin rate can allow us to determine how frequently pitchers are throwing pitches that contribute most to UCL injuries. One proposal is to track the number of high risk pitches thrown by each pitcher and imposing a cap on a pitcher's innings in a season [fangraphs.com], progressively lowering that cap for pitchers who throw more high risk pitches. Part of a pitcher's value to a team is their availability. If a pitcher is unavailable because they've reached their innings cap, they're less valuable to a team, providing an incentive to reduce the number of pitches thrown at high velocity and perhaps high spin rates. The proposed rule in the linked article focuses on fastballs, but a similar strategy could be applied to other high risk pitches.

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