The Baseball: The Proposed 2021 Changes and the Blue Jays

Media outlets have reported that MLB plans to introduce a new baseball for the 2021 season. How will the baseball be different? What is the likely impact generally upon play and the Toronto Blue Jays, specifically?

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The baseball used by MLB has undergone many changes in recent years. Still, most of those modifications have occurred with little notice. Let’s review the history of the post-2015 alterations and the impact upon both batters and hitters. With that context, we can understand what may happen with the 2021 baseball.


There was a surge in the number of home runs hit in 2015, 2016 and 2017 compared to 2014. The numbers were as follows: 2014 – 4,186; 2015 – 4,909; 2016 – 5,610; and 2017 – 6,105. The number of home runs in 2018 was lower (5,585) but 2019 roared back with 6,776. Hitters blasted 2,304 home runs in 2020’s 60-game schedule, translating into 6,221 taters over a 162-game campaign.

Follow the bouncing ball

Since 2014, the baseball used by MLB has undergone many subtle but impactful changes. The baseballs used in 2015, 2016, and 2017 were different than those used in 2014. The baseball used during the 2019 regular season was different from the 2015-2018 and 2014 versions. MLB utilized baseballs during the 2019 postseason that were different than the one that was in play during the 2019 regular season. Concerning the 2020 season, MLB used two distinct baseballs. Lastly, there is a proposal to change the baseball again for the 2021 campaign. I think Dick Allen foretold the future of the baseball in 1972.


Another point to bear in mind is that MLB partnered with a private equity firm in 2018 to acquire Rawlings, the sole provider of MLB baseballs.


When it comes to aerodynamics, I am a layperson. However, as baseball fans, we can understand the basic concepts. According to NASA, aerodynamics is the study of forces and the resulting motion of objects through the air.


Two terms are relevant to the flight of the baseball. First is the coefficient of restitution, which the Physics Factbook defines as the ratio of speeds of a falling object, from when it hits a given surface to when it leaves the surface. In baseball terms, the coefficient of restitution (“COR”) concerning the baseball is its bounciness. The higher the COR/ bounciness, the further a ball will travel after contact with the bat (all other factors being the same).


The most significant aerodynamic force that applies to nearly everything that moves through the air is drag, our second term. Drag is the force that opposes an aircraft’s motion through the air. Concerning the baseball in flight, the factors that influence its drag include the leather’s smoothness, the ball’s roundness, and the seams’ height.

The 2015-2017 Baseball

MLB addressed the 2015-2017 home-run explosion by creating a panel to study the causes of the change in home run rates. The collection of experts became members of The Committee Studying Home Run Rates in Major League Baseball. The committee issued its final report on May 24, 2018.


The key findings of the report are as follows:

  • The increases in home runs were primarily due to better “carry” attributed to changes in the baseball’s aerodynamic properties, specifically those affecting the drag.
  • The committee did not identify the cause of the decreased drag coefficient.
  • Data show the link between home run production and the relative humidity at which balls are stored.

Dr. Meredith Willis

Dr. Willis has a doctorate in astrophysics, is a knitter and a baseball fan. Hence, she was the perfect choice to study the baseball. Her first article appeared in The Athletic on June 6, 2018, and addressed the 2016 and 2017 baseballs. She has written subsequent articles for that media outlet as well as most recently for Sports Illustrated.


In the June article, Dr. Willis determined that the 2016 and 2017 baseballs’ laces were 9% thicker than those of the 2014 version. How does a thicker lace affect the distance a baseball travels? As Dr. Willis explained, Rawlings wets the leather covers before stitching the ball. The leather dampens the red cotton laces and, if allowed to dry under tension, the laces will remain stretched. A stretched lace creates bulges at the seams. However,  because thicker laces have greater tensile strength than thinner ones, a thicker lace will reduce seam bulges. Hence, Rawlings would produce a rounder baseball. Such a ball will have less drag and will travel a greater distance than the pre-2015 baseball.


Dr. Willis also surmised that the thicker laces “may have contributed to pitchers complaints concerning blisters via more “prouder” stitches creating a bumpier seam.”

The 2019 Regular-Season Baseball

In June 2019, The Athletic published another article from Dr. Willis, who examined the 2019 regular season baseball. Dr. Willis discovered that the seam height of the 2019 baseball was markedly lower than any ball since 2002. She postulated that there “is no doubt that lower seams would improve aerodynamics.” Furthermore, the leather cover on the 2019 regular-season baseball was smoother than previous models. “Like decreased seam height, this contributes to a lower drag efficient, making home runs even more likely. Also, slicker leather can be expected to produce the sort of grip issues being experienced by at least some pitchers”.


Dr. Willis, the knitter, returned to the topic of laces. In her investigation of the 2016 and 2017 baseballs, she attributed the rounder baseball in 2016 and 2017 to the thicker lace. However, the 2019 regular-season ball had thinner laces than those balls. The knitter concluded that Rawlings might have altered the manufacturing process by switching from air drying to hot airflow. By doing so, Rawlings would limit lace stretching, which accounts for lower seams, since tighter laces could potentially “hold seams down.”

The 2019 Postseason Baseball

There was an unexpected decrease in home-run rates in the 2019 postseason compared to the regular season. In an April 6, 2020 article for The Athletic, Dr. Willis examined a sampling of those baseballs and determined that MLB used balls from the 2018 and 2019 regular seasons. She concluded that there was nothing nefarious going on; MLB ran out of 2019 regular season balls and used what was in inventory from 2018’s production. The 2018 baseball generated a lower home run rate than the 2019 version.

The 2020 Baseballs

On February 9, 2021, Sports Illustrated published an article that examined the baseballs used in 2020; Dr. Willis provided the media outlet’s scientific analysis. According to Sports Illustrated, MLB used two variants of the baseball during the 2020 season. Both balls looked the same, including their respective seam height, similar to the balls used before 2019. However, Dr. Willis obtained a sample of 2020 baseballs and dissected them. Twenty-eight balls had centers similar to previous seasons; the other balls (fifteen) had centers that weighed 2.5 grams less than the separate batch. Dr. Willis named the former 2020N and the latter 2020L.


Wills opined that a lighter center would be smaller, thereby decreasing the average size of the ball. She concluded by stating that “a smaller ball has less drag, a 2020L would carry farther than a 2020N”.


Players themselves commented that some batted balls, which some thought were sure home runs, would land at the warning track during the season. Other batted balls sailed over the fence despite a similar swing. “It is no surprise players were confused. The 2020L and 2020N balls feel the same and look identical to the naked eye. The weight of their leather covers varies enough to camouflage the changes to the center. As long as the covers are on, it’s not possible to detect a difference, even with a sensitive scale”.

The 2021 Baseball

On February 8, 2021, The Athletic published an article written by Eno Sarris and Ken Rosenthal. The piece cited an MLB internal memo that notified teams that the 2021 baseball would be different from previous versions. The plan is to reduce the bounciness and the weight of the baseball.


However, experts differ on the impact upon ball flight due to the changes. One analyst said the relationship (COR reduction and distance) was linear enough to estimate that this change will reduce home run rates by around five percent. However, Dr. Willis opined that, if the ball is smaller, “you might expect drag to go down here.” In other words, “a ball that is deader coming off the bat but carries farther.”


The other item to note from the article is that five teams currently use humidors to store baseballs: the Mariners, Mets, Red Sox, Rockies and Diamondbacks. MLB expects five more teams to use humidors in 2021. According to public analyst Derek Carty, home run rates dropped by nearly 20 percent when balls retained their humidity.


I was surprised that MLB does not have a policy that requires teams to use a standard method of storing baseballs. With such a significant impact upon home run rates when teams kept baseballs in a humidor, why would MLB permit such team discretion?

What is the impact upon the Blue Jays?

For the sake of argument, let’s assume that the baseball’s proposed change will reduce home runs. What would the impact be upon the Blue Jays and the other Eastern Division American League teams?


One way to approach the question is to determine what percentage of runs scored for and against results from batted balls not in play. In 2020, the Blue Jays offence generated 51% of their runs from balls in play; 49% from balls not in play. The offence produced by the other division rivals from balls not in play are as follows: Rays – 46%; Yankees – 53%; Red Sox – 47%; and Orioles – 43%. By this measure, the Blue Jays are the team that is the second-most reliant upon home runs for run production. Therefore, the Blue Jays offence would be affected negatively by the 2021 baseball compared to three of its division rivals.


45% of the runs scored against the 2020 Blue Jays were via the long ball. This rate was in-line with most Eastern Division teams: Rays – 49%; Yankees – 52%; Red Sox – 45%; and Orioles – 45%. By this metric, the Rays and the Yankees would benefit the most from a home run reduction.

The Blue Jays and Statcast

Statcast categorizes batted balls into three segments.

  • No Doubters – a batted ball that would be a homer in any ballpark
  • Mostly Gone – a batted ball that would be a home run in eight to 29 stadiums
  • Doubters – a batted ball that would be a four-bagger in seven ballparks


The sum of No Doubters, Mostly Gone, and Doubters will not necessarily sum to the actual number of home runs. All No Doubters are home runs, but Mostly Gone and Doubters would be homers depending upon the stadium where that batted-ball event occurred.


In 2020, the MLB-average for No Doubters was 47%. For the Blue Jays, 38% of their home runs were No Doubters. Therefore, if the 2021 baseball is not as homer-friendly as prior seasons, the Blue Jays offence may be negatively affected. The negative impact would occur because of Toronto’s relatively low rate of No Doubters.


A sampling of No Doubters, as a percentage of actual home runs, for notable Blue Jays are as follows: Danny Jansen – 63%; Rowdy Tellez – 50%; Teoscar Hernandez – 44%; Bo Bichette – 40%; Lourdes Gurriel Jr. – 36%; Vlad Guerrero Jr. – 22%; and Cavan Biggio – 13%.


Toronto pitchers, including Robbie Ray’s time in Arizona, allowed 110 home runs; 45% were No Doubters. Therefore, if the 2021 baseball is not as homer-friendly as prior seasons, the impact upon Blue Jays pitchers may be minimal. The negligible effect is due to Toronto’s near-average rate of No Doubters in 2020.


As a percentage of actual home runs, a sampling of No Doubters for notable Blue Jays pitchers is as follows: Ross Stripling – 7%; Tanner Roark – 43%; Hyu Jin Ryu – 50%; Nate Pearson – 60%; and Robbie Ray – 84%.

The last word

MLB baseballs have changed many times since 2014. For the most part, those alterations contributed to a surge in home run rates. For the upcoming season, MLB has informed all teams that the 2021 baseball will have a reduced coefficient of restitution or, in a lay person’s words, less bounciness. This new baseball may reduce the distance travelled by the ball and lessen the number of home runs. However, some experts believe the new baseball may have a negligible impact on home run rates. For Blue Jays fans, it looks like the baseball is another ingredient to add to the mix for what should be an exciting 2021 season.




*Featured Image Courtesy Of DaveMe Images. Prints Available For Purchase.




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Bob Ritchie

Bob was a St. Louis Cardinals fan until the Blue Jays arrived on the baseball scene, although he still has a soft spot for the Cards. Similar to straddling the Greenwich Meridian, as depicted in the avatar, Bob applies sabermetrics when applicable, but his heart tells him that Lou Brock belongs in the Hall of Fame.