SAN DIEGO -- Major League Baseball's 2019 home run spike was partly a byproduct of microscopic variations to the ball itself -- that is, the height of seams -- as well as hitters attempting to hit more home runs because of an ongoing focus on launch angle and exit velocity.
This was the conclusion reached in an independent study commissioned by MLB that was done by Dr. Jim Albert of Bowling Green University, Peko Hosoi of MIT, Dr. Alan Nathan of the University of Illinois, and Dr. Lloyd Smith of Washington State.
Their findings were revealed in a 27-page report that was released on Wednesday, and the four scientists held a news conference at the Winter Meetings to discuss their findings along with executives from MLB and Rawlings, the company that manufactures the baseballs.
"I think one of the things we're going to have to do as we continue this journey of discovery is accept the fact that the baseball is going to vary and the performance of the baseball is going to vary, and we're going to do everything we can to control it," said Morgan Sword, MLB Senior VP, League Economics & Operations. "But that is kind of fundamental to the equipment choice we've made. I mean, it's always been the case. The baseball has varied in its performance probably for the entire history of our sport."
The committee's report said 60 percent of the home run increase could be attributed to a reduced drag from lower stitches, which leads to less drag on the ball and it traveling farther. And the other 40 percent was traced to a change in hitters' approach.
A complicating factor is figuring out how much of the reduced drag can be attributed solely to changes in stitching, as opposed to other factors.
"Seam height accounts for about 35 percent of change in drag," said Dr. Nathan. "Factors other than seam height account for the remaining 65 percent of the variation in drag, and unfortunately, we have not yet been able to identify these factors, despite lots of effort."
He discounted popular theories such as the baseball being more round or having a smoother surface or thicker stitches.
"None of these are correlated with drag," he said. "That's a firm result from the laboratory measurements. We conclude from all this that a baseball is actually a rather complicated object from the point of view of drag.
"It's very, very subtle, the effects that can occur. For example, in a pilot study that will be extended, we discovered that application of mud to the baseball actually has a significant effect on the drag. That particular study will continue."
The committee offered a series of recommendations, including studying how the rubbing of mud on balls before games influences drag. In addition, atmospheric-tracking systems will be installed to measure drag. Storing baseballs in humidor systems will be considered.
MLB sought the study during a season in which a record 6,776 home runs were hit, which was an 11 percent increase over the previous record, set in 2017. As to why home-run rates decreased in the postseason, the committee had no firm answers, noting the small sample size relative to the regular season.
"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," Dr. Nathan said. "So these are small effects, they're subtle effects, and they need rather sophisticated equipment in order to be able to measure them."
Rawlings President and CEO Michael Zlaket said the manufacturing process had remained consistent through the years.
"None of our processes have changed," he said. "There's always going to be some inconsistency in the product. It's created by the fact that it's natural materials, and the production process has a lot of manual steps, but I'm confident that we have always done it."
In a news conference later in the day, Commissioner Rob Manfred offered his perspective:
"I think the variability in the baseball is a product of the fact that it is a man-made product with natural materials. I think that's part of the charm of the game, and the reason that I'm prepared to live with that variability is both teams play with the same baseball.
"So in terms of the fairness and integrity of the competition, they got one ball that's out there at a time and they're both using the same one."