Has Baseball’s Pitch Clock Altered Players’ Injury Risk?

NEW ORLEANS — A new study reported here probably won’t end controversy over whether Major League Baseball’s “pitch clock” is causing more injuries, but it certainly provides food for thought.

No overall increase in ulnar collateral ligament (UCL) injuries could be discerned during the 2 years after professional baseball’s overseers introduced the pitch clock in 2023, according to Michael Andrew Mastroianni, MD, of NewYork Presbyterian Hospital in New York City.

But UCL injuries did afflict starting pitchers earlier in the season than was the average during the four full seasons prior to the pitch clock’s launch, and they seemed to be more common in starting pitchers as opposed to relievers, according to a poster he presented at the American Academy of Orthopaedic Surgeons’ annual meeting.

Mastroianni’s group, which included Christopher Ahmad, MD, head team physician for the New York Yankees, also identified other changes in pitching statistics coinciding with the pitch clock’s deployment. Whether or not the pitch clock was directly responsible for any of these changes, however, remains open for debate, insofar as Major League Baseball also implemented a variety of other rule changes in recent years, and team strategies have been evolving as well.

The pitch clock — an actual countdown clock mounted on the walls of every major league stadium — limits how much time a pitcher can take between pitches, an attempt to shorten games and keep fans in the seats and in front of their TV screens. It was tested in preseason games and then was fully deployed at the beginning of the 2023 season.

It didn’t take long for controversy to erupt. One of the game’s top stars, pitcher Max Scherzer, went public with complaints after the 2023 season was over, saying orthopedic surgeons had told him that pitchers’ elbow injuries had become more severe, and that the pitch clock was one contributor to this.

With more experience with the pitch clock, Mastroianni and colleagues decided there was enough data for a more rigorous look at the issue. Last year they reviewed a wealth of data — drawing on baseball’s almost comically detailed obsession with statistics — to examine what changes the pitch clock might have wrought.

They analyzed data from six full seasons from 2018 to 2024, excluding the pandemic-shortened 2020 season; thus, four seasons prior to the pitch clock and two with it in place. A bewildering array of pitching statistics and pitcher ratings were included: pitch velocity, spin rate, tempo, proportions of fast versus slow pitches, horizontal and vertical ball movement, how these varied with runners on base versus with bases empty, and with separate analysis for starters and relief pitchers. The poster compared averages from 2018-2022 to those from 2023-2024 — all in all, a great deal to fascinate baseball geeks.

But the principal stat that MedPage Today is here to tell you about is UCL injuries, for which the famous “Tommy John surgery” was invented (named after the star pitcher who was first to receive it, and whose career was saved).

In general during the four pre-pitch clock seasons, UCL injuries appeared to spread evenly over the April-October season, in the range of two to five each month (except in 2021, when 10 occurred in spring training in February-March). Once the pitch clock came in, though, a different pattern was seen; in 2023, there was a big spike in May, with 10 UCL injuries, before settling down to two to four later on. And in 2024, the monthly average was six from spring training through June and then dropped to two per month thereafter.

The other notable injury finding was that total UCL injuries were markedly higher in relievers versus starters prior to the pitch clock — about 70 per year versus 25 to 35 — but this pattern reversed in 2023-2024. UCL injury totals topped 60 in 2023 and came close to that again in 2024, a statistically significant increase (P<0.05).

Mastroianni and colleagues had a number of thoughts about these findings. “Starting pitchers may be ‘maxing out’ velocity expecting shorter overall innings,” they suggested, “which combined with more repetitions than relievers” — a starter typically throws 80 to 100 pitches before being taken out, versus maybe 30 to 40 for a reliever — “may make them particularly susceptible to fatigue.”

And looking at the increased early-season injury rates, the researchers argued that this “may signal a need to adapt spring training or early season workloads to account for the pitch clock changes.”

How might the pitch clock play into this? It has definitely shortened games, with most now completed in little more than 2 hours, although other rule changes have also contributed. “Previous research has demonstrated that faster pace-of-play rules may lead to enhanced flexor-pronator mass fatigue, potentially diminishing muscle recovery and lowering the injury threshold at an accelerated rate,” the researchers offered.

Still, other trends in baseball strategy may also factor in. It’s uncommon for starters to throw more than 100 pitches; they hardly ever pitch a full nine innings. That could explain the “maxing out” of velocity more than the pitch clock’s influence, as could an increasing emphasis on hard throwing (most pitchers, both starters and relievers, now routinely throw above 95 mph, which was phenomenal 30 years ago).

Other limitations to the analysis include that just two seasons of post-pitch clock data were available and few statistical comparisons in the study were statistically significant.