What We Can Learn From the KBO’s Juiced Ball Debacle
As first reported by The Athletic in February, MLB sent an internal memo to various team personnel announcing their intent to alter the construction of the baseball — specifically, to lower the COR (coefficient of restitution) by loosening the “tension of the first wool winding,” which slightly reduces the weight of the ball and thus makes it less bouncy. It’s a seemingly innocuous change that, based on MLB’s careful wordings, isn’t intended to dramatically change the league’s offensive environment.
But a different league overseas may suggest otherwise. The article’s authors shrewdly point out what happened over in the Korean Baseball Organization, when in 2019, the COR of its baseball was reduced “around .01 to .02 at most,” and the mass likely “reduced by less than 2.8 grams.” The subsequent effects, however, were profound. A hitter’s paradise that had thrived for several years vanished without a trace. Left in its wake were demoralized hitters whose batted balls died at the warning track instead of clearing fences.
Sung-min Kim once wrote about changes to the KBO’s official ball and how they reshaped the league’s offensive environment. Below is an updated version of some of his findings, now that the 2019 season is behind us. The conclusion is the same — a deadened baseball succeeded in suppressing league-wide offense, no matter how you put it:
What stands out is the sharp decline in slugging percentage. On average, KBO hitters went from batting like Tommy La Stella to Josh Reddick, in terms of wRC+, as a result of a different baseball. Batting average and BABIP also decreased as not just would-be home runs, but also would-be doubles and triples became outs.
When the 2020 KBO season finally commenced after much commotion, it seemed like a more balanced offensive environment would be here to stay. But what many discussions about the KBO leave out, including The Athletic article, is an unexpected development: In 2020, the balance once again tipped in favor of the hitters. During the first few weeks of the season, they absolutely demolished baseballs; batted balls that were home runs in 2018, then weren’t in 2019, were suddenly home runs again in 2020. Immediately, fans, analysts, and even players began accusing the KBO of tampering with the baseballs. Was something up? Not according to the KBO, of course, which concluded that there was insufficient evidence to claim that the COR of randomly selected and tested baseballs had changed.
This might seem suspicious, but the organization up to this point had been transparent about its handling of the official ball. After allegations against the Lotte Giants for using their own, juiced-up balls emerged in 2015, the KBO decided to implement a standardized official ball. And before the 2019 season, it announced to the public the extent to which the ball’s coefficient of restitution would be decreased. To be upfront for several years, then all of a sudden secretive seems odd.
That being said, the KBO might have also wanted to, without drawing too much attention, find a midpoint. The 2019 season was an ice-cold shock — the league ERA plummeted from 5.17 in 2018 to 4.17 in 2019, a difference of a full run. Nobody was prepared. That low 4-ERA mark might have been the ultimate goal, but perhaps achieved too soon, without sufficient time for hitters and pitchers to make adjustments. In three sets of data obtained by the Yonhap News Agency, the tested baseball averaged a COR of .4141. It’s down 0.86% from a test conducted in June of 2018, but — and here’s what intriguing — it’s also up 0.88% from a test conducted October of 2019. The sample size is on the smaller side (n = 36), but nevertheless leads credence to the idea that the KBO settled on an in-between ball. The assertion that there was insufficient evidence is based on the fact that the average COR still fell within the acceptable range (.4034 ~ .4234). But as three years have shown, even minuscule changes go a long way.
If finding a happy place in between 2018 and 2019 was the KBO’s ultimate goal, it did in fact succeed. Per the metrics introduced earlier, 2020 fell in between those two years:
The panic of May subsided, and as the months went on, the league settled into a stasis which drew minimal complaints from fans and players alike. Still, we don’t know if the KBO is solely responsible for the changes that occurred in 2020, or if the test results are a product of statistical variance. But perhaps we should also consider an alternative explanation. In an interview for KBS News, Byung-ho Park of the Kiwoom Heroes credited an extended off-season and better knowledge of the new official ball as reasons for hitters’ success.
“As the season was pushed back,” Park said, “there was time to prepare ourselves. He also added that “as much as the force of restitution decreased last year, hitters kept experimenting with the new ball, and that was a big help.”
Maybe Park is right. But as a hitter, he has a clear incentive to emphasize the resourcefulness of hitters while downplaying other potential factors. To wit, the news story in which the interview with Park is included also featured Hyun-seung Lee, a pitcher for the Doosan Bears, who mentioned that his teammates became wary of the situation after batted balls seemingly travelled beyond expectations. For pitchers, to accept that hitters have made adjustments is to accept an environment that is, from their perspective, harsh and unfair.
When we look at the numbers, though, it doesn’t seem like hitters in 2020 made any substantial changes compared to 2019 or 2018. This is an important caveat. A major reason why many are supportive of MLB’s efforts to deaden the ball is due to hopes that hitters will curtail their pursuit of home runs, thus reducing the number of strikeouts and increasing the number of balls in play. It’s a reasonable train of thought. Unfortunately, the KBO has set a precedent that might discourage fans of old-school baseball:
One positive takeaway, at least, is that the league’s strikeout rate did decrease from 2018 to 2019. However, it’s hard to conclude whether or not this change is a result of a different baseball. Despite a league-average wOBA of .349 in 2017, just two points below 2018’s mark of .351, hitters that year struck out 17.6% of the time, a number that falls more in line with 2019 and 2020. There’s no clear-cut correlation between strikeout rate and the offensive environment. In addition, the slight uptick in the percent of balls in play (InP%) is most likely due to the reduction in home runs — not because hitters changed their approach. As batted ball data is not available to the public in Korea, the ratio of fly outs to ground outs (FO/GO) serves as a crude, but decent proxy for average launch angle. If anything, the steady climb in FO/GO over the past three years reflects the KBO’s embracement of analytics and the importance of air balls, coefficient of restitution be damned. Want less strikeouts and more balls in play? A minor change to the official ball isn’t a viable solution, the KBO shows.
So what can fans of MLB take away from the KBO’s experience with its baseball? For one, to achieve the minor change MLB desires, the reduction in COR probably has to be smaller. The unexpected, sudden crash in league-wide offense that shook Korea warns us that we shouldn’t underestimate shifts of even hundredths. Second, this won’t be the last time MLB tinkers with its official ball. When we look back years later, it’s unlikely that the league will have accurately predicted the offensive environments in 2021 and beyond. There will be fewer home runs, sure, but to what extent? If the change is too sudden, what choice does MLB have but to alter the ball again? Lastly, a different baseball won’t stop hitters from swinging for the fences. In fact, as home runs become scarce, they will become even more valuable. This is what happened in Korea — the weighted run value of a home run was 1.857 in 2018, and the following year, it was 2.074. Unless the coefficient of restitution is lowered by extreme amounts, hitters will always be encouraged to pursue the long ball. There’s also no guarantee that strikeouts will fall and contact rates will surge as a result of a less lively ball.
But most importantly, we should realize that there is no one, simple solution. There never was, and never will be. And a different baseball certainly isn’t an example. The perceived problems with baseball are non-issues to others, or even aspects of the game they appreciate. As the KBO’s juiced ball debacle illustrates, it will take time and energy to arrive at a mid-ground which (mostly) satisfies fans, players, and those who work in baseball. A change to the official ball is potentially meaningless, maybe even detrimental depending on your stance. It is, however, a step in some direction. That beats going nowhere at all.
All statistics from Statiz.com, unless specified.
