A Look at Very Early 2021 Injury Trends

Just two months ago, Fernando Tatis Jr. signed a mammoth contract that will keep him in San Diego through 2034. He entered the 2021 season as arguably the most hyped player in the majors. We all breathed a collective sigh of relief when, after exiting a spring training game with shoulder discomfort, Tatis was cleared to resume play just a day later. Sadly, though, one of the game’s biggest stars was sidelined last week with a partial shoulder dislocation after taking a hearty swing at the plate.

On the heels of last year’s shortened season, fans and teams braced themselves for what they worried might be a bad year for player injuries. The season is entering just its second full week of action, but several notable players have already hit the Injured List, and this doesn’t even count the spring training losses of Eloy Jiménez, Kirby Yates, or George Springer:

Players push the boundaries of what is humanly possible on a daily basis. With each effort to reach the top of the Statcast leaderboards for fastball velocity or hard hit rate, there is a physical toll. Throwing a five ounce ball or swinging a 34 ounce bat as hard as you possibly can hurts — I’ve done this recently and I can confirm it’s uncomfortable. Doing so thousands of times over the course of a few months while staying healthy is a tall order.

Fielding and running the bases also pose risks to players’ health. Unless we’re talking about a home run trot, when the ball is in play, the players often sprint as fast as they can. It’s one reason why stolen base attempts are declining (analytics being the main culprit). It’s also why this potential fly ball out turned into a double:

Aaron Judge wasn’t sprinting for that ball and I’m willing to bet that the Yankees would rather have Trey Mancini record a double than have Judge miss time because he pulled a hamstring hustling to catch the ball (or worse, because he crashed into the wall). The recurring theme here is that baseball actions are often maximum efforts; these types of body movements are the most likely to cause injury.

Injuries are also sustained due to overexposure. Jiménez tore a pectoral muscle reaching over the fence to rob a home run. It’s a fairly uncommon type of play and sort of a fluky injury. Jiménez, not known for his defensive prowess, made an ill-advised effort. It was a spring training game for one, and his talents are best served when he has a bat in his hand. The point is that the more a team asks a player to do, the greater the likelihood that player will become injured.

This problem most clearly presents itself when pitchers in the National League are asked to bat, though this will presumably be the last season when they have to do so. Zac Gallen started the year on the IL thanks to a forearm stress fracture sustained while taking batting practice. You may also remember in 2019 when Max Scherzer famously took a foul bunt to the face, also during batting practice.

According to research conducted by Posner et al, injury rates on a macro scale have been on the rise for many seasons now. The study focused on injury data from the 2002 through 2008 seasons and found there was “a significant 37% increase in injuries between 2005 and 2008.” The injury rate from this period averaged 3.61 incidents per 1000 athlete-exposures. To put this in context, an athlete-exposure is equivalent to one rostered player in one game. For example, in one game today, there are presumed to be 26 (maximum allowable) rostered players per each team accounting for a total of 52 athlete-exposures. To figure the chance that one player on a roster for 162 games has to get injured, you would multiply the incident rate by (162/1000) or divide by about six. So, the average injury rate (3.61) for the 2002 through 2008 seasons equates to 0.58 injuries per 162 athlete-exposures. Another way to say this would be that, ceteris paribus, there is a little better than 50% chance that a player ends up on the IL.

The shortened season last year presented its own unique issues for player health. Another study done by Platt et al. analyzing the effect of the delayed start to the 2020 season on injury rates concluded:

“There was a significant increase in injury incidence for both pitchers and fielders in 2020. Injury rates increased in anatomic zones of the upper extremity and spine/core but were not significantly changed in the lower extremity. The overall increase in injury rate suggests that irregular or insufficient sport-specific preparation prior to the start of the season placed athletes at a greater risk of injury when play resumed.”

Per the study, injury rates for the last three seasons breakdown as follows:

The Platt study credited the spike in injury rates in the 2020 season to “limited physical preparation, lesser aerobic condition, and preseason strength deficits.” As such, it would be reasonable to expect the injury rate in 2021, a season that had a full, uninterrupted spring training, to fall back down to a rate similar to that of the 2019 season.

It has become a priority for teams to implement a host of strategies to reduce injury risk for their players. An excellent interview with Gary McCoy that aired earlier this week on Effectively Wild put the spotlight on using proper strength and conditioning to keep players on the field. Mike Petriello of MLB.com has also recently reported on the various strategies that teams plan to use to cover the innings load of a full season ranging from a six-man rotation to occasional use of a pair of tandem starters (piggybackers).

Is it possible to alter the increasing rate of injuries? The early season data so far looks promising. Through the first 12 days of the regular season, there have been a total of 37 non-COVID-19 related injuries. To put this in terms of recent studies, the calculated injury incidence rate for April 1 through 12 is 4.87 incidents per 1000 athlete-exposures. According to the Posner study, the highest frequency of injuries typically occurs in the first month of the season. Comparing the 2021 data to the first 12 days of previous seasons is pretty encouraging.

The 2021 data so far indicates that injuries are happening even less frequently than in the ‘18 and ‘19 seasons, with the injury rate during the first 12 days of those seasons about 20% higher than the average for the whole season. If the first 12 days of 2021 are a representative sample, the season injury rate could approach 4.00 by season’s end, which would be a huge reduction.

Comparing just the first 12 days of data doesn’t give us much certainty about how the injury rate will trend for the remainder of the season. The Platt study does lend some insight on the shortened season, but it doesn’t differentiate IL designations or days on the IL in its analysis. And while the injury rate is useful, it would be useful to better understand its correlation to injury severity and time spent on the IL. A few severe injuries that sideline players for long stretches may alter a team’s fortunes more dramatically than several 10-day IL stints depending on where they fall on the team’s depth chart. Additionally, the shortened season may impact player health in 2021 in ways we’re not aware of yet; a concern that is the focus of most teams this season is how their pitching staff will cope with handling nearly three times the amount of innings. It remains unknown whether or not players (especially pitchers) will struggle more to stay healthy in the second half of the season after having adapted to the lighter workload in 2020. What we can hope for, though, is that last season’s spike in injuries has motivated teams to take a more structured approach to planning around injury prevention. The shorter season did give players a reduced workload from what they typically experience over the course of 162 games. The early season data suggests that, at least so far, the additional rest may have done them some good.