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MLB has released a report on the 2019 baseball

The ball was different and so were players’ approaches to it

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Baseballs from a game in September
Darren Yamashita-USA TODAY Sports

Home run rates have been generally out of control for the past few seasons, I’ve written about this a few times here, but honestly you don’t need to go back to my pieces on how 40 home runs isn’t what it used to be or my look at the number of clubs who absolutely demolished their home run records in 2019. You can see the rate increase clearly in this chart:

Yearly home runs per batted ball 2000-19
MLB Report

I don’t know that anyone needed a chart to see that the home run rate had increased dramatically over the last few seasons, but it’s still alarming to see the rate of increase.

There have been a number of studies and articles that have looked at the home run surge and the baseball to try and figure out the cause of the surge. Specifically, Dr. Meredith Wills has been at the forefront of independent analysis of the baseball with her work for the Athletic. I highly recommend you read her June piece which identified two main findings. First, the 2019 ball was, in fact, demonstrably different from previous years. Additionally, the 2019 ball had differences that were distinct from the changes in the ball that caused the 2017 surge. She joined us for the 17th episode of our podcast, and answered a bunch of questions about her work. It’s worth checking out the interview, that conversation taught me just more about the physical baseball than just about anything else.

For it’s part MLB has maintained that they have not deliberately changed the baseball. Last July, Commissioner Rob Manfred had this to say to the Baseball Writers’ association of America:

“Baseball has done nothing, given no direction for an alteration in the baseball,” Manfred told the Baseball Writers’ Association of America on Tuesday. “The biggest flaw in that logic is that baseball somehow wants more home runs. If you sat in an owner’s meeting and listened to people talk about the way our game is being played, that is not the sentiment among the owners for whom I work. There is no desire on the part of ownership to increase the number of home runs in the game. To the contrary, they’re concerned about how many we have.”

In that same availability Manfred noted that they would be reconvening a group of experts to study the baseball and the home run surge. That report was released today and included the home run graph above.

Before we jump into the results of the most recent MLB study I think it’s worth noting that this is the second time in three seasons that MLB has had to convene a group of experts to study the baseball. That is stunning in and of itself. You can read the May 2018 report on the 2017 surge here. With that as the backdrop, let’s take a look at what today’s MLB study found:

After analyzing StatCast data and 65 dozen unused baseballs MLB’s panel found that there were significant ball-to-ball variations in drag that were correlated to seam height. Notably, seam height was one of the variables Dr. Wills highlighted in her earlier work. They also found that the ball was responsible for approximately 60 percent of the home run increase on 2018-19. In an article by Craig Calcaterra in Hardball Talk Wednesday, Dr. Wills elaborated on her previous comments:

Specifically, she concluded that seam height and decreased bulging of baseballs which led to less aerodynamic drag and farther ball flight was likely the result of Rawlings using heaters to dry balls, as opposed to the traditional air-drying, allowing them to produce more balls in a shorter period of time. Wills told NBC Sports this morning that she suspects Rawlings did this because many more balls were needed due to Major League Baseball mandating that Triple-A adopt the major league ball for the 2019 season.

As such, the key word in this morning’s report is “intentional.” Wills:

“The decrease in drag was very likely unintentional, but the change in the drying process would be intentional. No, they didn’t intend to juice the ball, but yes, they did make an intentional change to the manufacturing process. It was not ‘manufacturing variability’ it was deliberate process improvement to accommodate higher demand. ‘Variability’ makes it sound like it’s random or a mistake. It was not.”

The remaining 40 percent of the increase was found to be the results of “launch conditions.” The paper defines launch conditions as the approach players are taking at the plate.

This scientific study can’t conclude that “launch conditions” were impacted by the changes in the ball, in fact, it explicitly states:

Lacking strong evidence that the change in launch conditions are due to changes in the baseball, we conclude that they are due to a change in player behavior.

I agree with this conclusion for the purposes of this study, but I think it is worth pointing out that after seeing home run rates jump for three of the previous four seasons players and coaches concluding there should be a different approach at the plate would be a logical reaction to changes in the ball. It seems unlikely those changes occurred in a vacuum.

In addition to releasing data on factors impacting home run rates this report also offers recommendations for the league and teams going forward. Those recommendations are below:

  1. Rawlings should develop a system to track the dates on which balls are manufactured and shipped to clubs. Clubs should log which batches of baseballs are used in which games or homestands.
  2. To facilitate determination of drag and other properties affecting performance from in-game data, MLB should install atmospheric tracking systems at field level in all 30 parks, including temperature, pressure, relative humidity, and wind conditions.
  3. Since changes in drag play a major role in driving changes in home runs, MLB should codify the current procedures used to monitor the drag, whether in the laboratory or with in-game data, sampling baseballs manufactured throughout the production cycle.
  4. Similarly, the monitoring of other baseball properties (especially the COR and CCOR) at UMass/Lowell, which is currently being done 9 three times each season, should be expanded to sample baseballs manufactured throughout the production cycle.
  5. In view of the apparent dependence of drag on the applied mud based on measurements of a small sample, a more extensive study should be performed with much larger sample.
  6. MLB should study the viability of employing humidors in all 30 parks to reduce the variability in storage conditions across the league.

I’m a pretty big fan of the recommendations that look at data, quality control and manufacturing. I’m also a little shocked that those processes weren’t already in place. I’m a lot more skeptical of the recommendation that all ballparks adopt the humidor, which seems like a solution that could have any number of unintended consequences across the league. The goal here isn’t to make the ball play identically in Chicago as it does in San Francisco, the goal is to just know what to expect from the baseball for purposes of fielding the most competitive baseball team possible.

Here is the full report in PDF form if you’re interested.