Do Injury Rates in Position Players Who Convert to Pitchers in Professional Baseball Differ From Players Who Have Always Been Pitchers?
Yesterday, I found myself in the operating room performing a Tommy John surgery on a professional pitcher — nothing unusual about that, except for the story behind how he ended up on my table. This pitcher didn’t start his professional career on the mound. In fact, he began as a catcher, a position that requires an entirely different set of skills and physical demands. But one fateful day, during a blowout game, his team’s bullpen was running on fumes, and with no other options left, they asked him to step up and pitch the last couple of outs.
The situation of catchers being asked to pitch isn’t as rare as one might think in the big leagues, and it’s a scenario that often unfolds during the most lopsided of games. When the bullpen is depleted, and the game’s outcome is all but decided, managers sometimes turn to their most unlikely pitchers: the catchers. These moments, while lighthearted, often leave a lasting impression and sometimes even change the trajectory of a player’s career, as it did with the pitcher I recently operated on.
Take Russell Martin, a former Yankee catcher, for example. The former All-Star catcher is known for his prowess behind the plate, but in 2019, while playing for the Los Angeles Dodgers, he found himself on the mound during not one but two blowout games. In both instances, Martin pitched a scoreless inning, baffling hitters and reminding everyone just how versatile catchers can be. Despite never being a full-time pitcher, his effectiveness in those situations speaks to the catchers’ athleticism and baseball acumen.
Erik Kratz, another journeyman catcher, had a similar experience with the New York Yankees. In 2020, during a blowout loss, Kratz took the mound and threw a scoreless inning. It was one of those moments that fans love — an unexpected twist in an otherwise forgettable game where a catcher takes on the unfamiliar role of pitcher and performs admirably. Kratz’s outing wasn’t just a novelty; it was a testament to the deep understanding of the game catchers develop, making them surprisingly effective when called upon to pitch.
Sandy León, a veteran catcher, also found himself on the mound more than once. In 2021, while with the Cleveland Guardians, León pitched a scoreless inning in a blowout game, just as he had done in 2019 with the Boston Red Sox. These appearances, though rare, highlight the unique role catchers play — they’re often the last line of defense, stepping up in ways few others can when the situation calls for it. Chris Gimenez and Jeff Mathis also belong to this rare group of catchers who’ve taken the mound. Gimenez, known for his versatility as a backup catcher, pitched several times throughout his career, often stepping in to save an overworked bullpen during games that were out of reach. Similarly, Mathis, another seasoned veteran, pitched a scoreless inning for the Texas Rangers in 2019, adding his name to the list of catchers who’ve moonlighted as pitchers.
Famous Converted Players
Is it really possible for position players to master the art of pitching so late in their careers without years of specialized training? Let’s dive in. Some of the most successful pitchers in Major League Baseball didn’t start their journeys on the mound — they started elsewhere, playing different positions, only to pivot to pitching and completely redefine their careers.
Take Joe Nathan, for instance. Drafted as a shortstop by the San Francisco Giants, Nathan initially struggled at the plate. But when he was converted into a pitcher, everything changed. He didn’t just adapt — he excelled, becoming one of the most dominant closers in the game and racking up 377 saves over his career. Then there’s Trevor Hoffman, another legend of the bullpen, who also began as a shortstop. When his powerful arm proved better suited for the mound, he transitioned to pitching and saved over 600 games, solidifying his place in baseball history.
Kenley Jansen’s story follows a similar arc. Originally a catcher for the Los Angeles Dodgers, Jansen’s raw arm strength caught the attention of his coaches, who saw his potential as a pitcher. The move paid off, as Jansen became one of the league’s most feared closers. Sean Doolittle’s journey is just as remarkable — once a promising first baseman, Doolittle’s career was sidetracked by injuries. But instead of fading away, he found new life in the bullpen, where his velocity and command turned him into an All-Star closer.
These stories aren’t just about learning new skills — they’re about the unpredictability and resilience that define baseball careers. Sometimes, a player’s true potential only emerges when pushed into an entirely new role, proving that it’s never too late to discover a new path to success.
Converted players who had and did not have TJ Surgery
As a Tommy John surgery specialist, I’m constantly digging for clues to understand why the UCL, that crucial ligament in the elbow, gives out so often. The stories of Joe Nathan and Sean Doolittle offer some insight. Both started their careers as position players before leaping over the mound, where they found success. But even their journeys weren’t without setbacks. Nathan, for instance, tore his UCL during spring training in 2010, a moment that led to the grueling road of Tommy John surgery. Yet, he didn’t just come back — he returned to dominate, proving that even after such a significant injury, it’s possible to reclaim greatness.
Sean Doolittle’s path was strikingly similar. Known for his powerful arm and laser-like control, Doolittle faced the same daunting surgery in 2023. Like Nathan’s, his story reminds him of the physical toll pitching can take, even on those who didn’t start their careers on the mound. It’s a testament to the role’s demands and how, no matter where a player begins, the strain of pitching can eventually catch up.
Then there’s Trevor Hoffman, another player who transitioned from shortstop to the mound. Unlike Nathan and Doolittle, Hoffman avoided Tommy John surgery throughout his career. Over 600 saves later, his ability to stay healthy stands out as extraordinary — a testament to his durability and career longevity. Hoffman’s journey is a reminder that while the risks are always there, some players manage to navigate them.
The question
When I finished the Tommy John surgery on my patient, who had transitioned from catcher to pitcher, it brought back memories of another converted player I operated on years ago. That case left me with a question that has lingered ever since. Given the steep learning curve and the intense demands on your arm, does switching to pitching later in your career increase your risk of UCL injuries? Or is it possible that you have an advantage — less risk — because your elbow hasn’t endured the years of relentless wear and tear that lifelong pitchers accumulate from day one?
The research
To explore the intriguing question of whether players who switch to pitching later in their careers are at more or less risk for UCL injuries, we conducted a research study with the backing of the Major League Baseball (MLB) Research Committee. We focused on professional baseball players who transitioned from position players (infielders, outfielders, and catchers) to pitchers between 2011 and 2018.
These converted pitchers formed the core of our study group. To provide a meaningful comparison, we created a control group of pitchers who had been pitchers since their professional careers. We matched each converted pitcher with a control pitcher based on several factors — draft round, age, level of play, and dominant arm — ensuring a fair comparison between the two groups.
Injury data for both groups was meticulously gathered from the MLB Health and Injury Tracking System (HITS) database. Established in 2010, HITS is a comprehensive league-wide injury surveillance system that records player injuries and time lost due to those injuries. It has been used in numerous studies and is recognized as a reliable source of information on player health.
We calculated the number of injuries per year for each player. For the converted pitchers, we only considered injuries after their pitching transition. For control pitchers, we started counting from the year they signed their professional contracts. The duration of each player’s career in terms of available performance data was also factored in to determine how long each player was at risk for injury. We didn’t stop at just injury rates — we also compared pitching performance between the two groups.
Results
Our study took a deep dive into the careers of 221 professional baseball players who leaped from position players to pitchers between 2011 and 2018, with 23 reaching the major leagues. In terms of performance, converted pitchers started fewer games, pitched fewer innings, and had slightly worse WHIP (walks plus hits per inning pitched) compared to control pitchers. This is not surprising as converted pitchers don’t have the training resume that the non-converted pitchers have.
What we found with injuries was indeed interesting. The control group — those who had been pitchers all along — didn’t just have more injuries overall; they also had more injuries per year compared to the converted pitchers. 78% of the lifelong pitchers sustained injuries, while only 54% of the converted pitchers did, a difference that’s not just noticeable but statistically significant. Additionally, the types of injuries differed between the groups, with control pitchers more likely to suffer shoulder and elbow injuries, while converted pitchers had a more varied injury profile.
Now, the question is why?
It likely comes down to the miles they’ve logged on their arms. Every pitch, every fastball, every curveball — each one has the potential to add a little more wear, a little more tear, especially on the elbow. Over time, that accumulated stress becomes like a ticking clock, counting down to when something finally gives. Those who’ve been on the mound since they were kids might already be carrying around enough damage to make future injuries feel almost inevitable. It’s the classic story of cumulative workload — how years of repetitive stress push the body to its limits and, sometimes, beyond.
This raises some tough, essential questions, not just about pitching but about how we approach sports. Is early sports specialization — when young athletes focus on one sport year-round, honing their skills to perfection — the best path? And more specifically, what about early pitching specialization? We often celebrate the prodigies, the kids who can throw heat before they can drive, but what toll is that taking on their developing bodies?
The body, after all, is resilient, but it’s not invincible. You’re playing a dangerous game when you start loading up the arm with thousands of pitches before it’s fully matured. The elbow, with its complex web of tendons and ligaments, wasn’t designed to endure that kind of repetitive strain at such a young age. The miles add up quickly, and by the time these young pitchers reach the big leagues — or even just college ball — they might already be approaching the limit of what their bodies can handle.
So, what’s the alternative? Should we encourage more varied athletic development, letting kids play multiple sports to build overall strength and reduce the risk of overuse injuries? Or should we rethink the way we train young pitchers, perhaps further limiting pitch counts more strictly or delaying the introduction of certain pitches until the body is better equipped to handle them?
These are tough questions with no easy answers but crucial ones. Because the goal isn’t just to create great pitchers — it’s to create great pitchers who can have long, healthy careers. And that means we need to think not just about the here and now but about the long-term impact of every throw, every game, every season. It’s about understanding that the path to greatness doesn’t have to be a straight line and that, sometimes, the best way to protect a young arm is to give it a break.
