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The World Baseball Classic Injury Effect

DL stints have already shaken up the MLB season, and some are blaming WBC participation. But are the critics right to say that the tournament causes injuries at a disproportionate rate? We dug into the numbers to find out.

(Getty Images/Ringer illustration)
(Getty Images/Ringer illustration)

This year’s World Baseball Classic was a massive spectator success. For the first time in the tournament’s short history, which has spanned four events over 11 years, the games were streamed on MLB.TV, which made them more accessible. In another, on-field first, the United States went all the way, which left the home crowd for the finals happy even as the whole world was dazzled by dramatic comebacks, displays of passion, and an array of international talent that included, most notably, Puerto Rico’s Carlos Correa–Francisco Lindor–Javier Báez infield (not to mention the Mensch on the Bench).

In the span of a few weeks, the discourse surrounding the WBC changed, as we went from reading about non-participating players trashing the tournament to reading about other non-participating players reconsidering their stance for 2021. If the FOMO stays strong, the next edition of the WBC could feature the richest rosters yet.

Sending more prominent players to a big stage at a slow time for the sport sounds like a good thing for baseball, but it’s likely to lead to an increase in the most common complaint about the exhibition tournament: the injuries it may cause. Every time the tournament takes place, players get hurt during WBC action, and some fans blame (or possibly scapegoat) the event for the casualties. The more stars suit up for future tournaments, the more likely it is that the WBC will be deemed responsible for a season-altering injury to a high-profile player.

This year’s toll from the tournament wasn’t disastrous, but there were still several injuries that might make some fans frightened to see their teams’ stars depart the supposed safety of the Grapefruit and Cactus Leagues. Yankees shortstop/Netherlands second baseman Didi Gregorius suffered a shoulder strain while playing out of his typical position and will be out for April, while Martín Prado (Venezuela) and pitchers Drew Smyly (U.S.), Seth Lugo (Puerto Rico), and Roberto Osuna (Mexico) all started the season on the disabled list after seeming to sustain new injuries or to aggravate old ones while appearing in the tournament. Mariners starter Smyly is on the 60-day DL with a strained flexor tendon and Mets pitcher Lugo will miss weeks at a minimum with a slightly torn UCL, which could handicap two teams that projected to be on the playoff bubble. And even though the tournament is long over, there’s no statute of limitations on accusing the WBC of contributing to injuries that occur in-season, such as the groin injury Félix Hernández suffered on Opening Day.

The question, of course, is whether the WBC actually makes injuries more likely. Players get hurt all the time during spring training, too: This year alone, a long list of hitters (Ian Desmond, J.D. Martinez, Jason Kipnis) and pitchers (David Price, Alex Reyes, Trevor May, Carlos Rodon, Sonny Gray, Collin McHugh, Steven Matz) who didn’t play in the tournament are sidelined nonetheless thanks to spring injuries. It’s plausible that the extra emotion, effort, and early preparation involved in the WBC, along with a lack of direct supervision by each participant’s full-time team, do elevate injury risk. But anecdotal examples can’t confirm that, no matter how frustrating it feels when a player gets hurt while wearing a different uniform. Even the players who get hurt during WBC games don’t always blame the WBC; Gregorius, for instance, wouldn’t say that his injury happened because of the WBC, while Osuna said outright that his didn’t.

Last week, Ken Rosenthal relayed some statistics from Major League Baseball that seem to show that the WBC is more of a healing balm than a health hazard. MLB’s data show that the rate of season-opening DL stints among players on 40-man rosters who didn’t appear in the WBC has been far higher than the rate among those who did. Obviously, though, there’s a huge, honking caveat here: Players don’t go to the WBC unless they’re believed to be fully healthy, whereas many players who stay in spring training are still recuperating from serious injuries or dealing with nagging ones that rule them out of tournament play. The fact that more non-WBC players start the season on the DL tells us that teams purposely aren’t letting previously injured players participate in the WBC, but it doesn’t tell us much about whether the WBC causes injuries at a disproportionate rate.

For that, we need different research. Late last month, three members of the Wash U Sports Analytics group (Adam Kaufman, Sam Linker, and Jacob Gross) did a study on WBC injury rates in which they compared the number of days each WBC participant spent on the disabled list in the season immediately following his WBC appearance with the average number of days the same players spent on the DL in the three seasons preceding their WBC year and the three seasons after, wherever applicable. For example, if a player participated in the 2013 WBC, his DL days in 2013 would be compared with the average of his DL days from 2010 to 2012 and from 2014 to 2016. (If a player wasn’t active over the whole seven-year sample, any years when he was active were included in the calculations of the overall averages.) If the WBC injury effect is real, we would expect the number of DL days in the WBC year to be higher than the average from the surrounding years.

The trio’s initial research seemed to confirm a small WBC effect of roughly three DL days per player, but before considering the issue settled, I contacted Kaufman and suggested a few tweaks to the study. Instead of the DL data used in the original study, we switched to the comprehensive injury information collected by athletic trainer Corey Dawkins and published at Baseball Injury Consultants. Dawkins’s data includes day-to-day injuries in addition to DL stints, and minor league injuries as well as major league injuries. We also included all injuries instead of excluding "freak" ones such as bone breaks, concussions, and torn ACLs, because unpublished research by FiveThirtyEight writer Rob Arthur suggests that so-called freak injuries follow the same pattern that other injuries do. (Players with more freak injuries in their pasts suffer more freak injuries in their future, possibly because their style of play puts them at risk in certain ways.) And lastly, in addition to comparing the WBC players with themselves, we also compared the WBC players’ results with those of a non-WBC control group.

The results of the self-comparison are consistent with a slight WBC injury effect, but they’re far from airtight proof of one. Overall, WBC pitchers lost about four more days to injury during their WBC years than they did during the surrounding seasons. WBC hitters, meanwhile, lost slightly less than one more day to injury during their WBC years. (Full results are available here.)

All told, we’re talking about a WBC group of a little more than 200 hitters and a little fewer than 200 pitchers across the three WBC seasons combined, small enough samples that the results could be skewed by one unlucky year. If so, 2009 could be the culprit. That year, WBC pitchers (led by Jorge Campillo, Scot Shields, and Edinson Volquez) lost 10.1 days compared with their surrounding seasons, and WBC hitters (led by Alfredo Amezaga, Carlos Delgado, and José Reyes) lost 5.7. If we exclude 2009 and combine the results from 2006 and 2013, though, the WBC injury effect seems almost nonexistent: Pitchers lost 1.3 days during those WBC years, and hitters were actually healthier, with 2.0 fewer days lost.

The control-group results cast further doubt on the WBC injury effect. In the one year preceding their WBC appearances, WBC pitchers and hitters averaged 14.6 and 16.1 days lost to injury, respectively. Again using Dawkins’s data, we came up with a list of 82 pitchers and 90 hitters who had lost between 10 and 20 days to injury in the same pre-WBC seasons as the WBC players, but who did not go on to play in the WBC. These players didn’t necessarily have the same track record of health over an extended stretch that the WBC players did, but they were coming off roughly equally healthy single seasons. (The control group averaged 16.2 and 16.5 days lost to injury, respectively, in the pre-WBC season.)

The results reveal that the control-group pitchers, who didn’t pitch in the WBC, saw their days lost to injury rise even more during the WBC year than the WBC pitchers did. For hitters, the difference was close to the same.

It’s possible that the healthy, pre-WBC season was more uncharacteristic for the control-group players than the WBC players, which could make the control group’s post-WBC declines more dramatic. But if you take any group of players who were particularly healthy in one season, those players are likely to be less healthy the next, whether they play in the WBC or not. Although the subject deserves further study as the sample expands, the perceived WBC injury effect could be a product of regression to the mean, coupled with selective memory that makes WBC injuries stand out in our minds more than those sustained in the course of spring training.

It’s understandable that team officials would "remain wary of the WBC," as Rosenthal wrote. Teams have many millions of dollars tied up in their players’ well-being and the outcome of the regular season, and the loss of a single pivotal player such as Smyly can derail a winter’s work and lead to lasting frustration, even if the GM (in this case, Jerry Dipoto) declines to publicly point a finger at the WBC. For now, though, the evidence of an injury effect isn’t strong enough to justify preventing players from participating, especially since a well-populated tournament is so much fun for fans — and, in the long term, potentially beneficial for baseball, which in turn enriches teams.

Thanks to Corey Dawkins, Adam Kaufman, Sam Linker, and Jacob Gross for research assistance.