It wasn’t a juiced ball. It was a drag show.
A group of scientists tasked with finding the reason home runs flew at a record rate in Major League Baseball last season believe the ball’s aerodynamic properties – and particularly the drag on its surface – are the culprit and not changes to the core that would cause extra bounciness, according to a report the league released Thursday.
In the midst of a season in which players hit a record 6,105 home runs and emboldened juiced-ball theorists, MLB commissioned 10 scientists to study the source of the spike. Using a combination of Statcast data and laboratory testing, the group found that balls in 2016 and 2017 had lower drag coefficients than their predecessors.
What they didn’t find was why.
“It was something of an unsatisfying result,” said Dr. Alan Nathan, a physicist who has studied the game for decades and chaired the group that wrote the 84-page research paper. “We had a set of baseballs that had a much higher than average drag. We had a set of baseballs that had a much lower average drag. We asked ourselves: ‘What’s the difference between these baseballs?’ ”
Nathan’s conclusion: “We cannot find a single property that we can actually measure other than the drag itself that would account for it. … We do admit that we do not understand this.”
Unsatisfying though the result may have been, the report spells out in clear detail the rigor with which the scientists approached the testing. Considering everything from the pill at the heart of the ball to the surfeit of players seeking to hit the ball at a higher launch angle, they combed troves of data to eliminate certain possibilities while still considering others.
The specific aerodynamic culprit remains elusive – and, the study showed, it behooved everyone from power hitters to not-so-powerful hitters. Generally speaking, as a ball travels through the air, it is slowed by air molecules bouncing off it. Without drag, Nathan said, a 400-foot home run might travel 700 feet. As the group tested batches of balls from four time periods – pre-All-Star Game 2015, post-All-Star Game 2015, 2016 and 2017 – “what we saw was a progressive decrease in the drag properties,” Nathan said.
The Sports Science Laboratory at Washington State, where the studies were conducted, will continue to research the cause of the drag loss. Additionally, the group recommended MLB standardize storage conditions for game balls in all 30 stadiums, meaning the humidors used in Colorado and Arizona could be replicated elsewhere. The other definitive takeaway: Tighten the specs on the coefficient of resistance, or the bounciness of the ball, which, Nathan said, “is so large it’s a meaningless statement.”
The variability of the COR still was not evidence enough to blame the core. Three members of the group went to the Costa Rican factory where Rawlings produces major league balls to vet the manufacturing process. While a number of pieces along the supply chain have changed in recent years, none, the group determined, explained the spike in home runs. Neither did the height of the seams, which could have had an effect on drag but in lab tests didn’t.
It found the clearest evidence in Statcast data. There is a sweet spot where a player can hit a ball with a certain exit velocity and launch angle that makes a home run far likelier: between 90 and 115 mph at a 15- to 45-degree angle. Using a data set of 337,881 batted balls from 2015-17, the group noticed a significant change in the results of balls hit near those parameters year over year. Particularly from 95 to 105 mph and 20 to 40 degrees, the data set showed an increase in 403 home runs from 2016-17.
The takeaway was clear: The balls were flying differently.
Was it the weather? Well, the group looked at data from Tropicana Field in Tampa Bay, a domed stadium with consistent conditions, and it verified not just what the larger set said but what lab testing showed, too. Maybe the rubbing mud used to take the sheen off brand-new balls? It’s probably not the determining factor, but it could be enough of one that the scientists suggested the league ensure the balls are rubbed more uniformly.
Perhaps the most intriguing theory – and one the group hopes to test further – involved the pill, or core, of the ball. The idea was that the more centered the pill is, the more aerodynamically sound the ball would be. If it’s even a centimeter off-centered, the ball could wobble – imperceptibly to the eye but enough to add to the drag coefficient.
This theory is particularly rich because of its implications: That the workers who make the balls by hand in Costa Rica – who wind the pill, who cut and stitch the leather, who take pride in their craftsmanship – have gotten so good at making perfect baseballs with pills in the exact center of the ball that it’s going farther accordingly.
It may be a stretch. Nathan doesn’t know. None of the scientists do.
“Absolutely I’m disappointed,” Nathan said. “Do I like having to tell you guys we don’t understand that? I don’t like having to tell you that. However, as a scientist, the data are what the data are, and we have no control over it. We certainly aren’t going to BS our way through it and pretend we know what we don’t know. And we don’t know. From my point of view, it’s dissatisfying, but it’s not entirely unexpected.”
Without an answer, the testing will continue, and perhaps it can resolve the newest question: Why, after a nearly 50 percent jump in home runs from 2014 to 2017, are homers are down 10 percent this year?
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