SAN DIEGO — In the wake of a record-setting season for total home runs — 6,776, or 1.39 per team per game, an increase of 21.4% relative to last year, and 11.0% relative to the previous record, set in 2017 — on Wednesday morning, Major League Baseball released its long-awaited report from a committee of scientists and Rawlings representatives in their attempt to account for what has happened during the 2017-19 seasons. Shortly afterwards, an eight-member panel consisting of representatives from the committee, Rawlings, and MLB then fielded questions from the media. It was a lot to absorb, even given familiarity with the topic, but the general impression from all that’s been put forth is that MLB and Rawlings don’t have the firmest of grips on their product and its performance.
The full 27-page “Preliminary Report of the Committee Studying Home Run Rates in MLB” (PDF) is highly technical, and worthy of further scrutiny, scientific study, and perhaps skepticism, but a few things came through in the press conference and a cursory trip through the report. First, Rawlings and MLB denied that there’s anything underhanded when it comes to changing the ball. Said President/CEO of Rawlings Michael Zlaket, “We have never been asked to ‘juice’ or ‘de-juice’ a baseball. And we’ve never done anything of the sort. Never would.”
Second, beyond a reiteration of the committee’s 2018 finding (PDF) that the ball-to-ball variability in aerodynamic drag is greater than the year-to-year change in average drag — a consequence, the league and Rawlings maintain, of using a product made of natural materials and constructed in part by hand — is that even the scientists involved in MLB’s committee are still grappling with the complex interplay of factors that affect drag. Seam height plays the biggest role, but hardly the only one. It will take further study to untangle the other factors — work that both Rawlings and MLB say that they’re committed to doing, via the committee.
In the press conference, Dr. Alan Nathan, professor emeritus of physics at the University of Illinois and one of the scientists on the committee, gave a lengthy introduction that broke the report’s findings down into layperson’s terms (transcript via ASAP Sports):
So here are the principal things that we found. First, let me address the Statcast analysis, which shows that the home run increase in 2019 was due both to a decrease in the drag, that is, improved carry. That accounted for roughly 60 percent of the increase, and changes in launch conditions accounted for another 40 percent of the increase.
By the way, in 2018 home runs were down. The drag was actually higher although the launch conditions were more favorable. So you had two effects going in the opposite direction.
So regarding the drag, both the laboratory experiments that were done on large samples of baseballs and the Statcast data continued to find both large ball-to-ball variation and smaller year-to-year variations of the drag, just as we found in our initial studies.
Now, in looking for the properties of the ball that are responsible for the variation in drag, the laboratory data show a clear correlation between drag and seam height. This is something that escaped our observation in the preceding study simply because the equipment that we were using was not precise enough to determine that, but with the improved equipment, we could do that. So we see a correlation both ball-to-ball within any given year as well as correlations from year to year.
Now, seam height is definitely one of the things that — the changes in seam heights certainly related to some of the changes in drag, but only about 35 percent of it. Just to give you an idea, the change in seam height of a fraction of the thickness of a sheet of paper like this would give you a measurable effect in the change in the drag. So these are small effects, they’re subtle effects, and they need rather sophisticated equipment in order to be able to measure them.
During the presser, one reporter asked, “You mentioned 65 percent of the source of the drag is unknown. Roughly how long would it take you to potentially find the source of that, and what would that process be like?” Answered Dr. Lloyd Smith, a professor of mechanical engineering from Washington State University:
“We have no idea. (Laughter.) We’re working very hard on it, and we’ve got support from MLB, and motivation, so it’s going to be a very active process for us. But at the conclusion of our last report, we knew the drag had changed, we didn’t know why, and we didn’t know how long it would take us to find the answer. We didn’t know if it was because of the accuracy of our measurements or if it was because of some phenomenon that we hadn’t yet considered that we needed to consider.
“So we just have to go back through that process again, refine what we’ve done, look at other ideas, and talk to other people and take lots of measurements.”
The committee’s report concludes, “No evidence was found that changes in baseball performance were due to anything intentional on the part of Rawlings or MLB and were likely due to manufacturing variability,” but the word intentional is doing a lot of work in that sentence. It’s fair to question how a league that owns about 25% of a manufacturing company whose processes have apparently changed could make that claim, but then Rawlings and MLB are also claiming that their processes haven’t changed, which ought to raise eyebrows as well. Writing for The Athletic in June, Dr. Meredith Wills, the leading independent scientist when it comes to examining the construction of the baseball itself, cited the Home Run Committee’s previous reports of numerous changes from 2014-18 involving the yarn, pill, leather, and drying process, and suggested that MLB’s wording was a matter of semantics:
“[T]hings like enhancing leather smoothness or drying baseballs more efficiently might not be considered ‘meaningful’ [commissioner Rob Manfred’s word] to manufacturing.
“While this may have been a reasonable attitude in the past, such enhancements now appear to have compounded, producing a more aerodynamic ball.”
Dr. Wills took issue with several aspects of the new report, particularly with regards to its lack of transparency and refusal to acknowledge research that wasn’t their own. Summarizing the big picture, she told FanGraphs:
The report states that carry (presumably the ball) made a 60% contribution to the 2019 home run surge. However, very little information was provided on the methods used to study the ball and come to their conclusions, which is problematic considering some of their conclusions (i.e., discounting a number of specific physical characteristics as not contributing to decreased drag). Dr. Barton Smith [professor of mechanical and aerospace engineering at Utah State University, not to be confused with Dr. Lloyd Smith] and I have provided extensive detail on our methods of studying physical properties of the ball, making our results verifiable and reproducible. The exploratory committee report provides too little information to validate their methods and findings.
For an example, Dr. Wills cited the report’s claim that “Novel tests of the baseball were devised and conducted” without elaborating on methodologies, citing a previous on-the-record comment to her from MLB chief communications officer Pat Courtney and MLB Senior Vice President of League Economics and Operations Morgan Sword about the use of “destructive testing” (taking balls apart). She noted that Dr. Barton Smith had recently blogged about an experiment providing observational evidence of the physics connecting seam height and drag. Considering the nature of the finding, she expressed surprise that the result was not specifically cited and only indirectly referenced as “studies…of other investigators,” with a link to the overall blog.
Dr. Wills also called “ridiculous” an assertion made by one committee member during the press conference that the group had not seen any tests relating to the relative smoothness of the leather of recent baseballs. In her aforementioned June article, which was widely circulated throughout the industry, Dr. Wills found statistically significant measures of static friction demonstrating that the leather covers from 2019 balls were genuinely smoother than those from 2018 as well as other samples going back as far as 2000.
In November, Dr. Wills delved into the mysteries surrounding the baseballs used in the postseason, which, per the work of Baseball Prospectus‘ Rob Arthur, produced massive variations in average coefficients of drag and thus, carry and home run frequency, variations likely attributable to using different batches of baseballs. Having deconstructed several “official postseason baseballs” obtained directly from Rawlings and deciphered the batch codes, she found that many were repurposed inventory, either from out-of-spec 2019 or late-2018 balls. On that subject, Dr. Wills told FanGraphs:
The main thing is that (as with the 2017 ball) the committee took Rawlings’ word that the manufacturing process was the same for regular- and postseason. The implication is that they mean 2019 regular season and 2019 postseason, although the vague wording would also mean that regular season balls from any year could be used in the postseason. They state that the regular season drag coefficients vary year-to-year. They also find inexplicable higher drag for the postseason.
Considering my findings (which, granted, are not game balls) that 2018 balls were stamped as 2019 postseason plus the statement from Rawlings’ CMO that it is standard practice for Rawlings to use blanks from previous seasons as part of their on-field (i.e., game) ball population, the committee should have performed their due diligence and questioned the manufacturing dates of the postseason balls.
Doubtless the report will fuel Dr. Wills, Dr. Smith, Arthur, and others to take a closer look at the committee’s claims. As noted, we almost certainly haven’t heard the last on this topic from the league, either. Prior to the conclusion, the committee’s report makes half a dozen recommendations for further and more extensive studies to monitor drag and other physical properties of the ball, ranging from how batches of balls are stored, to how the mud is applied prior to those balls being used in games. Said former major league pitcher Chris Young, a panelist who is now MLB’s Vice President of On-Field Operations, Initiatives, and Strategy, “In addition to accepting the recommendations of the committee, we’ll remain focused on controlling the sources of variability as best we can, including the mudding application process, the shipment, and the storage conditions.”
We can hope that all of this leads to more consistent balls, but Rawlings and the league do seem resigned to some of the realities of variability that come with their product. In a question pertaining to how major league pitchers will accept the findings of the committee, Young said, “[O]n any given night, my job was to be better than the opposing pitcher. Ultimately, if you’re both pitching with the same baseballs and playing with the same baseballs, then you have to be better, and that’s what our sport is about, and that’s your responsibility.”
That’s not likely to mollify those studying the balls. Wrote Wills, “I’m not sure how to reconcile the promises of tighter specs, improved oversight, and the insistence that they can make predictable changes with the repeated insistence that ball-to-ball variability is so massive and so unavoidable that it makes it (apparently?) impossible to figure out how the ball has changed.”
Arthur called the “playing with the same baseballs” statement “disingenuous,” and touted a piece of his own in reaction to the report, which was published at Baseball Prospectus on Thursday morning. In it, he noted that the report confirmed his findings regarding drag in the postseason. He dug into the report’s exploration of changed batter behavior, the altered hitting style commonly referred to as the “launch angle revolution,” suggesting an earlier timeline than the report did (more 2017 than ’18) and seizing upon the impacts of both ball-to-ball and year-to-year variation, which aren’t just matters of scientific quibbling:
In explaining the results of the study, MLB took a tack of noting that changes in drag from one year to the next are small compared to the difference between any pair of baseballs. That’s true, but it’s nothing we didn’t know before, and it makes the findings the committee observed sound minor when they aren’t. After all, if year to year variation is smaller than something else, maybe it isn’t such a big deal after all?
This defense is empty because it’s usually the case that when you compare a pair of samples of multiple measurements, variation is smaller than for any individual data point in the sample. In this case, individual balls vary in their flight by up to 30 feet, whereas annual averages differ by a mere 5-10 feet.
But both represent major issues for MLB. The former, ball to ball variation means that a pitcher could grab one baseball that would become a certain home run, while the ball next to it would be an easy flyout. Any given postseason game or pitcher start could be made or broken by the particular baseball they happen to get in that moment
Year to year variation is also important because it means that we have a different version of baseball every season. That’s been the case in each of the last five years, with home runs shooting up to their highest rate ever, TWICE, punctuated by a brief return to only a merely very elevated home run tally. Sure, the yearly variation isn’t like the 30 foot jumps or falls a hurler goes through from pitch to pitch, but that’s not exactly a standard to aspire to, either. From the perspective of a fan or player who just wants an even playing field over time, both ball to ball and year to year variation represent significant issues.
All of which suggests that everybody — the league, teams, players, analysts, and fans — may have to contend with what Arthur called “a roller-coaster ride of longball rates, abrupt changes from month to month, and epidemics of pitcher blisters” going forward. Buckle up.
Brooklyn-based Jay Jaffe is a senior writer for FanGraphs, the author of The Cooperstown Casebook (Thomas Dunne Books, 2017) and the creator of the JAWS (Jaffe WAR Score) metric for Hall of Fame analysis. He founded the Futility Infielder website (2001), was a columnist for Baseball Prospectus (2005-2012) and a contributing writer for Sports Illustrated (2012-2018). He has been a recurring guest on MLB Network and a member of the BBWAA since 2011. Follow him on Twitter @jay_jaffe.