Study Concludes Seam Height Changes Contributed To 2019 Home Run Spike

SAN DIEGO—Major League Baseball announced Wednesday the conclusion of its study into the increased home run rate during the 2019 season.

Among the findings, a committee of scientists determined changes in the drag of the baseball and other launch conditions were primarily responsible for the rise in home runs in the both the major leagues and Triple-A, which switched to using the major league ball in 2019.

The committee of scientists determined a drop in the average seam height of less than 0.001 inches was responsible for 35 percent of the decrease in drag on the ball.

The committee said it could not identify the factors responsible for the other 65 percent of the decrease in drag.

“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,” said Lloyd Smith, a professor of mechanical engineering at Washington State and one of the report’s authors. “But at the conclusion of our last report (in 2017), 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 study also found no evidence that changes in the baseball were due to anything intentional on the part of Rawlings, which manufactures the ball, or MLB.

“We have never been asked to juice or de-juice a baseball,” Rawlings president and chief executive officer Michael Plaket said, “and we’ve never done anything of the sort.”

Teams combined to hit a record 6,776 home runs in 2019, up from 5,585 in 2018. The study attributed 60 percent of the home run increase to the ball’s improved carry and 40 percent to the changes in launch conditions, namely player behavior to increase their launch angles and exit velocities.

The study’s authors also addressed the decrease in home runs in the 2019 postseason, saying no changes were found to have been made to the baseball between the regular season and postseason, even though the committee found the drag was lesser in the postseason.

The study concluded the seam height between the balls used in the 2019 regular season and 2019 postseason were the same, and thus could not identify the reason for the change in drag that led to fewer home runs during the playoffs.

“Laboratory measurements confirm that the drag is higher, but interestingly, there is no change in seam height between the postseason baseballs and the regular season baseballs for 2019,” said Alan Nathan, a professor of physics emeritus at Illinois and another of the study’s authors. “Once again, it shows that there are things that we really do not yet understand about what are the contributing factors to drag.”

As far as the home run increase in Triple-A, Rawlings representatives said there were no changes made in the production of the ball, including the drying of the baseballs, in order to fulfill larger orders to supply enough balls for both the major leagues and the Triple-A leagues.

The two Triple-A leagues saw a combined 5,752 home runs hit in 2019 after switching to the major league ball. They two leagues combined for 3,652 home runs in 2018 using the minor league ball.

“None of our processes have changed,” Plaket said.


The committee’s report made six recommendations:

  1. That Rawlings develop a system to track which balls are shipped to clubs and that clubs log which batches of balls are used in each game or homestand.
  2. That MLB install atmospheric tracking systems at all 30 parks to determine drag and other properties affecting performance from in-game data.
  3. That MLB codifies the procedures used to monitor the drag on the ball
  4. That the monitoring of the baseball’s properties, currently conducted three times a year at Massachusetts-Lowell, should be expanded to sample baseballs throughout the production cycle.
  5. That a larger, more extensive study be conducted on the mud applied to the baseballs.
  6. That MLB study the viability of employing humidors in all 30 parks to reduce the variability of storage conditions across the league.

MLB senior vice president Morgan Sword said he believes the league will accept all of the committee’s recommendations. Notably, he said MLB is working with Rawlings on developing a baseball that does not require mud application.

“We’ve been working with Rawlings to develop a kind of pretacked baseball that doesn’t require mud application,” Sword said. “That is a fairly long process. One, to develop a product that’s suitable, and then to get it in the hands of players and coaches to test it.

“We have made some progress on that in the last couple of years. I think the other option is to proceed with the current ball and do a better job of standardizing the way we apply mud to baseball. Last year we actually implemented a set of standards for each club to follow in how they apply mud to baseballs before the game. I think coming out of this report, we’re going to look to enhance and enforce those standards a little more rigorously.”

Sword, however, also noted that some level of variability between individual baseballs is inevitable given they are hand-stitched and made from natural materials.

“What I’ve taken from this and learned from (this committee) is that we choose to use a piece of equipment in our game that is made of natural materials and hand-stitched” Sword said, “and that introduces a lot of variability into that piece of equipment that wouldn’t exist if it was fully synthetic or something that was made with less human involvement.”

“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, but that that is kind of fundamental to the equipment choice we’ve made.”

Commissioner Rob Manfred, speaking after the committee, said MLB had no plans to move to a synthetic ball that could remove that variability.

“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,” Manfred said.

“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.”

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