Major League Baseball recently released its official report investigating the source of last season’s home run surge. The independent committee concluded that the cause was the ball itself—specifically, a decrease in the ball’s drag coefficient. However, they were unable find the reason for this change.

After taking apart and examining twenty-six baseballs, not only have I found a possible explanation for the decrease in drag, but one that could also account for the recent spike in pitcher blister injuries.

Working under the hypothesis that pre-2015 balls are structurally different than 2016-2017 balls in some way, I systematically disassembled two populations of baseballs—twelve from 2014 and fourteen from 2016-2017. A Major League baseball is made up of a core (the “pill”) surrounded by five layers: an inner layer of thick grey yarn; a middle layer of white yarn; an outer layer of thin grey yarn; a thin layer of cotton thread; and a leather cover. The cotton thread is held in place by glue, while the two pieces of the leather cover are stitched together by red laces.

To gather my data, I removed the leather covers by unstitching the laces, rather than cutting them. I then cut away the cotton thread layer (as the glue made unwinding the thread untenable), carefully unwound and separated the three yarn layers, and removed the pill. The photo below shows the disassembled materials in comparison with an untouched baseball.

The various components of a deconstructed baseball, as compared to an intact ball. (Photo: Meredith Wills)

The goal was to keep the construction materials as intact as possible, so they could be measured and compared. Ultimately, I recorded sixteen independent variables, shown in the graphs below. For the most part, the findings were consistent with those presented in the official MLB report. While some individual components showed a wide scatter, there were no statistically significant differences between the 2014 balls and the 2016-2017 balls… except in one case.

(Above: The sixteen independent variables measured for this study. The results from the 2014 baseballs are shown red; those from the 2016-2017 baseballs are shown in blue. The central point is the average value, with error bars of one standard deviation.)

The laces in the newer baseballs are different—noticeably different. Those used to stitch the seams on the 2016-2017 balls are 9.0% thicker than those on the 2014 balls.

Lace thickness was measured using a variation on the “Wraps per Inch” method commonly found in fiber arts. Since the laces are so thin, measurements here were done in “Wraps per Centimeter.” In the example shown below, the laces from a 2014 ball wrap 40 times over 3 cm, whereas the 2017 laces wrap 36 times over 3 cm. As the units for “Wraps per Centimeter” are 1/length, thicker laces will produce a lower value. Converting “Wraps per Centimeter” to actual lace thickness, 2014 baseballs have laces with a thickness of 0.78±0.03 mm, whereas 2017 laces are 0.85±0.023mm thick.

A comparison of lace thickness measurements from a 2014 ball and a 2017 ball, using the “Wraps per Centimeter” method. (Photos: Meredith Wills)

Despite the small values, 9.0% makes for a noticeable increase in tensile strength, and such a change can’t help but affect aspects of the ball.

“We did not take any baseballs apart the way that you did,” said Alan Nathan, a Professor Emeritus of Physics at the University of Illinois and the chair of the independent committee commissioned by MLB, when asked about these findings via email. “However, we did ask Rawlings all the changes made in the construction process starting in 2014. The laces were not among the changes made.

“It’s not so easy to predict how thicker seams might affect the drag coefficient,” Nathan said. “I suspect it might. However, I would not easily be able to predict whether the drag would be larger or smaller.”

At the very least, thicker laces are easier to grip and therefore lace more tightly, potentially producing a slightly smaller baseball. While not statistically significant, both the data in the graphs and the data in Figure 38 of the MLB report show a trend towards smaller ball circumferences after 2014.

In addition, thicker laces are less likely to fray and break, and do not “stretch” as easily. Fraying untwists thread to a certain extent, causing it to lengthen. This property is often taken advantage of by pitchers, who pick at the seams to “raise” laces asymmetrically. A decrease in breakage and fraying means the ball is less likely to permanently deform as a result of impact. In effect, after contact with the bat, balls stitched together with thicker laces are more likely to “snap back” to spherical symmetry.

This introduction of thicker laces could very well be the factor that led to the home run surge. According to the executive summary released by MLB’s independent committee, “[M]anufacturing advances that result in a more spherically symmetric ball could have the unintended side effect of reducing the ball’s drag.” While it is unclear how much spherical symmetry would be gained from a 9.0% increase in lace thickness, it is unreasonable to assume that it would not make some contribution to drag reduction, thereby allowing the ball to carry farther.

Another likely consequence of thicker laces is the “epidemic” of pitcher blisters that began in 2016. Increased lace thickness will produce slightly prouder stitches (not to be confused with seam height, which is related to lace tightness and cover fit), creating a “bumpier” seam. Since blisters are often associated with tightly gripping or rubbing the seams, the rougher texture could be a strong factor in higher rates of blistering. In fact, the possibility of thicker stitches was even postulated by pitcher Rich Hill last year, although the follow-up was minimal.

Clearly, the advent and reason for this change to the baseball should be examined in more detail.

“I think some wrong conclusions about the baseball were made by others based on over-interpreting measurements from a small sample size,” said Nathan. “…Our committee had the advantage of much larger sample sizes. Having said that, you may be on to something.”

Measuring larger samples across a longer time span should show if lace thickness has increased systematically, or in “jumps.” The latter might suggest changes in the manufacturing process by Rawlings’ supplier; if the change was not reported by that supplier, it is quite possible that Rawlings was not even aware the baseball had changed. In addition, a comparison of drag coefficients on “control groups” of baseballs with different lace thicknesses might make it possible to quantify the extent to which lace thickness affects drag. Those same control populations could also be used to test the relationship between lace thickness and pitcher blister rates.

Regardless, it would appear that a small and unlooked-for change to the ball may be having a dramatic impact on multiple aspects of the game. One might even call it baseball’s “batter-fly effect.”

Special thanks to Martin Alonso, Rob Arthur, Phillip Buck, Will Carroll, Ben Lindbergh, Alan Nathan, and Eno Sarris for their insight and assistance.

(Top photo: Jake Roth-USA TODAY Sports)