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Saturday, December 14, 2019

The Pen: What does MLB do next about its inconsistent baseball? A scientist explains

Several things can be true at once, and self-serving explanations can be valid or at least compelling. For example, when commissioner Rob Manfred says at the winter meetings that the variability of the ball is “part of the charm of the game” which he is uninterested in fully eradicating, this is a rhetorical departure from his earlier public position emphasizing that the balls all meet specifications, that the specifications will be tightened, and that effectively everything is under control. But also, maybe the variability is part of the charm of the game — or at least, it could be.

Asked about the potential of adopting a more stable, synthetic baseball, Manfred made his stance abundantly clear. “I would not, am not now, and would not be in favor of moving away from the baseball that has traditionally been used to play what I regard to be the greatest game in the world,” he said this week in San Diego.

So then the imperfect ball is here to stay.

And Major League Baseball, perhaps realizing that the media was not going to drop it or else recognizing that it cannot control a man-made production down to one-thousandth of an inch, has pivoted to extolling the virtues of variability — which is not an entirely disingenuous venture for a sport played in open-air weather conditions within inconsistent field dimensions.

Is it just me, or do all these claims about the baseballs only serve to raise more questions?


QLE Posted: December 14, 2019 at 12:27 AM | 11 comment(s) Login to Bookmark
  Tags: juiced baseballs

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   1. bobm Posted: December 14, 2019 at 10:07 AM (#5908671)

And perhaps the league, which has previously attempted to quell focus on how different balls seemed to travel different distances despite the same force applied at the same angle, was particularly moved to embrace this aspect of the game now because the new report released by a committee of independent scientists this week revealed not just variance between the average baseball season-to-season but an even more significant variance among individual balls within seasons.

Really? That's the new story? In-season variability is the problem? Not gopher balls?

Pay no attention to the commissioner behind the curtain.
   2. Jose Is Absurdly Chatty Posted: December 14, 2019 at 10:21 AM (#5908673)
Variability is fine. Having everything be perfect and precise is not a feature. Some uncertainty about what is going to happen is a good thing.
   3. Greg Pope Posted: December 14, 2019 at 11:19 AM (#5908679)
I'm in favor of robot umps and replay (although not the current implementation). And I have no problem with some variability in the ball. However, it needs to be centered around something different than today.

It seems like the suggestion I've seen here about slightly less bounce, but significantly more drag would be ideal. Still reward hard hit balls, but reduce the home runs.
   4. Jay Seaver Posted: December 14, 2019 at 12:09 PM (#5908684)
Again, wasn't the previous explanation that the new balls weren't variable enough - that the manufacturing process had gotten refined enought hat all of the balls were winding up at one end of the acceptable range?
   5. bunyon Posted: December 14, 2019 at 12:22 PM (#5908689)
At least two teams are moving fences in. MLB doesn't seem to think HR rate is a problem.
   6. Walt Davis Posted: December 14, 2019 at 02:13 PM (#5908710)
Read Manfred as "Of course MLB retains the right to tinker with the ball in whatever direction we think will put more butts in seats."
   7. bobm Posted: December 14, 2019 at 02:21 PM (#5908712)
2018 "Report of the Committee Studying Home Run Rates in Major League Baseball"


The following summarizes the principal findings that result from our research and analysis:

1. The number of home runs per batted ball in MLB has increased steadily over the period 2015-2017.

2. StatCast data show that the increases in home runs are primarily due to better “carry” for given launch conditions (exit velocity, launch angle, spray angle) as opposed to a change in launch conditions. The better carry results in longer fly ball distances for given launch conditions and therefore more home runs. Analysis shows that the better carry is not due to changes in temperature but rather to changes in the aerodynamic properties of the baseball itself, specifically to those properties affecting the drag.

3. There is supporting evidence that the aerodynamic properties of the baseballs have changed, both from laboratory measurements and from analysis of StatCast/Trackman trajectories, both for pitched and batted balls. Additionally, a physics-based model for the flight of the baseball shows that small changes in the aerodynamic properties of the baseball that are comparable to the measured changes in the drag coefficient since 2015 can explain the observed increase in home run production over the periods studied.

4. There is no evidence that the observed decrease in drag coefficient is attributable to a change in a property of the baseball that is currently tested by Rawlings or UMass/Lowell,including the size, weight, and seam height. While it cannot be ruled out that small year-to-year variations in these properties might be a minor contributing factor to the home run surge, these changes are within normal and expected manufacturing variation. There is no evidence that such variations occur either intentionally or through substandard quality control by Rawlings, but are inherent to the manufacturing process, which relies on substantial“by hand” labor.

5. The committee has not yet succeeded in definitively explaining the cause of the decreased drag coefficient beginning in 2015. Various hypotheses have been proposed and tested, including gradual changes in the manufacturing process affecting the centering of the pill within the baseball or the deformation of the baseball while spinning. There is an ongoing effort to develop more precise measurement techniques to investigate these hypotheses. [...]

9. The yearly reduction in average drag, which accounts for the change in the home run rate, is small compared to the variation in drag among baseballs within a given year, leading to our recommendation (see below) that MLB develop testing procedures and standards for the aerodynamic properties of baseballs.

10. While Rawlings has periodically replaced aging machinery and made minor changes in a few processes since the start of 2014, there is no evidence that these changes have contributed to the home run surge.

11. Suggestions that changes in batter behavior (e.g., “pull hitting” or trying to hit the ball at a higher launch angle) might be contributing to the surge are not borne out by the StatCast data. There has been no significant change in these aspects of batter behavior that correlates to an increase in home run hitting.

12. Analysis of StatCast data shows that the home run surge is “global”, affecting players throughout the spectrum of home run hitting ability. [...]


The following summarizes the recommendations of the committee to the BOC:

1. Since changes in the carry of a fly ball have played an important role in the home run surge, MLB should work with Rawlings and/or independent test labs to develop methods to measure and monitor parameters of the baseball that affect the carry. This should include using the parameters, with fixed initial conditions, to monitor and control changes in carry distance.

2. MLB should monitor the climate environment (temperature, humidity) at which clubs store their baseballs. Given that this environment can have a significant effect on the COR and CCOR, MLB should require clubs to store the baseballs in a controlled environment that does not change over time.

3. MLB should monitor and attempt to standardize the application of mud on the baseballs, since the surface texture of the baseballs affects drag.

4. MLB should re-evaluate the specifications on parameters of the baseball that affect the game, such as size, weight, COR, and CCOR. They should also relax specifications on features that are unimportant, such as the color of the pill. Finally, they should require Rawlings to do impact testing of the pill at speeds producing deformations similar to those expected under game conditions rather than the low-speed drop test currently done.

5. Rawlings should be encouraged to develop and apply statistical methods to monitor the long-and short-term trends of their test data as part of their quality control procedures.

6. MLB should continue to study the drag properties of baseballs, with the goal of elucidating the reasons for the large variation of these properties among baseballs.

7. MLB should continue their efforts to improve the overall completeness and accuracy of the StatCast data, which were an important resource for the analysis leading to the findings in this report.
   8. bobm Posted: December 14, 2019 at 02:42 PM (#5908718)
2019 "Preliminary Report of the Committee Studying Home Run Rates in MLB"

3 Findings

3.1 What Baseball Properties Affect Drag?

1. The improved experimental measurements reveal a ball-to-ball correlation between Cd [coefficient of drag] and seam height (Fig. 2) with R2 ≈ 0.35 in addition to a strong correlation between the yearly-average Cd and seam height for the four periods encompassing the years 2013-2019 (Fig. 3).

2. Other than seam height, none of the other alternate hypotheses discussed in the media (e.g., roundness, surface roughness, lace thickness) are correlated with Cd. Factors other than seam height account for roughly 65% of the ball-to-ball differences in Cd, and have been relatively constant between 2013 and 2019. An example is shown in Fig. 4

3. Given the large ball-to-ball variation and the comparatively small yearto-year changes in both Cd and seam height (Fig. 5), large sample sizes (≈ 20 dozen) are needed to compare yearly changes using current test methods.

4. The aerodynamic flow over a baseball is complex [4], resulting in drag properties that depend not only on seam height but also on spin rate,
spin axis, seam orientation, application of mud (see Fig. 6), and possibly other factors not yet identified. While we have learned much from our studies as well as those of other investigators [5], there is much that is not yet understood.

3.2 What Drives the Home Run Changes?

1. The StatCast data were analyzed using the technique described by Albert [6] to separate the home run changes into two parts: a part due to changes in carry [i.e., drag] and a part due to changes in launch conditions [i.e., ball-bat interaction]. [Emphasis added]

The following results are obtained (see Figs. 7-8 and Table 1):

• For 2016-2017, the increase in home runs is primarily due to an increase in carry, as previously concluded in the 2018 report [1].

• For 2017-2018, the change in home runs is due to two opposing effects: a change in launch conditions, which would have increased the number of home runs; and a decrease in carry, which would have decreased the number of home runs. The combined effect was a decrease in home runs.

• For 2018-2019, approximately 60% of the home run increase is due to an increase in carry and 40% to a change in launch conditions. As noted above, only 35% of the increase in home run rate attributable to greater carry is due to a change in the seam height.

[...] Moreover, the pattern of changes during the period 2016-2018 from laboratory measurements (Fig. 3), with much smaller samples sizes in 2016 and 2017, do not follow the pattern from StatCast data (Fig. 9). These discrepancies are puzzling and perhaps point to the need for larger sample sizes, such as those available for 2018-2019.

4. Both Cd [coefficient of drag] values and fly ball distances show considerable variation about their mean values (Fig. 10), qualitatively consistent with the ball-to-ball variation in drag found in laboratory experiments. However, for given exit velocity and launch angle, the variation of fly ball distance with rate of backspin and sidespin on the batted ball is much larger than the variation due to Cd (Table 2). Whether year-to-year changes in those spin rates play a role in the changes in home run rates is currently under investigation.

5. Some of the home run increase is due to the changes in launch conditions.
• Not only is there a general increase in home run hitting, but the rates of hitting home runs has shown a general increase across players of all slugging abilities (see Fig. 11).
• The parameters contributing to this change are exit velocities, launch angles (see Fig. 12), and spray angles.
• From analysis of the Rawlings and UMass/Lowell test data (Fig. 13), there is some evidence of a small increase in the CCOR of the baseball between 2018 and 2019. However, that increase was too small to play a significant role in the home run increase in 2019. • 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. [Emphasis added]

3.3 Did the Home Run Rate Change in the 2019 Postseason?

1. It is the understanding of the committee that Rawlings uses the same manufacturing process to create the baseball used in the postseason as they do to create the ball used in the regular season, save for the application of the postseason stamp. There would therefore be no reason to 8
suspect a change in the performance properties of the baseball between the regular and postseason. [...]

While the analysis controlled for home field, the sample size was far too small to control for players in any meaningful way.

3. The laboratory testing showed a comparable increase in Cd but no change in seam height for the 2019 postseason baseballs compared to the 2019 regular season baseballs. Therefore, the reason for the change in Cd for the postseason baseballs is not known.

4. It should be noted that there are far fewer games played in the postseason than during any given week of the regular season. For example, there were 37 postseason games in the 2019 postseason, compared to typically ∼ 90 in any week of the regular season.

3.4 Recommendations

Based on its investigations, the committee makes the following recommendations:

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 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.
   9. bobm Posted: December 14, 2019 at 02:56 PM (#5908720)
Craig Calcaterra:

Dr. Meredith Wills, an astrophysicist who has been conducting her own research on baseballs and the home run explosion, published her own work on all of this in The Athletic last June. Wills concluded that, based on her examination of baseball seams and seam height, a key part of the manufacturing process — the drying of damp, finished baseballs after assembly is complete — likely did change.

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.”

   10. "RMc", the superbatsman Posted: December 15, 2019 at 10:42 AM (#5908783)
7-9: TL, DR.
   11. bobm Posted: December 15, 2019 at 10:38 PM (#5908893)
[10] 7-9: TL, DR.

7: HR increase in 2015-2017 due to baseballs having less aerodynamic drag, not change in batters' approach. No one knows what Rawlings did, because no one systematic tests the aerodynamic properties of the baseballs being made, distributed to teams, and being rubbed with mud.

8: By 2018, the continued HR increase is now driven by two factors: (i) baseballs having less aerodynamic drag and (ii) a change in batter's approach. If you think the baseball changed in the 2019 postseason, you do not understand small sample size, statistics, or randomness. Still, no one tests the aerodynamic properties of the balls. (It's like sabermetrics has entirely skipped the Commissioner's Office.)

9: Astrophysicist says Rawlings changed the drag on the ball unintentionally by intentionally changing the manufacturing process to meet demand. (If only someone systematically measured the aerodynamic properties of the baseballs being made...)

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