MLB on home run spike: Balls not juiced, but had greater aerodynamic carry

Gabe Lacques | USA TODAY

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A study commissioned by Major League Baseball indicated that baseballs used from 2015-2017 were not juiced, but that “changes in the aerodynamic properties of baseballs” resulted in greater carry and a home run surge during that period.

While no definitive reason was given for the shift, MLB Commissioner Rob Manfred issued a list of recommendations Thursday that the league will follow, most notably exploring whether humidors will be used to store baseballs in all 30 ballparks.

The 10-person committee released results of its study Thursday, and found that Rawlings, which manufactures baseballs for MLB, “achieved much greater precision than allowed by the MLB specifications” regarding parameters such as weight, size, and and the ball’s COR (coefficient of restitution).

It conducted laboratory testing of 15 dozen unused balls from 2013 to 2017, and 22 dozen game-used balls from 2012-2017. StatCast data, which became available in 2015, was utilized to measure batted ball behavior based on launch angle, exit velocity and other factors.

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Notably, it ruled out a change in batter behavior – the so-called “fly ball revolution” that prompted many hitters to swing with a more pronounced uppercut – or pitch selection.

Instead, wrote committee member and theoretical physicist Leonard Mlodinow, “the home run surge is not due to a bouncier, juiced ball, or to a change in batter behavior, but to better carry, which result in longer fly ball distances, and therefore more home runs.

“The question now becomes, why has this happened?”

While the study group did not reach a conclusion to that query, Manfred, in a statement, said he is “accepting their recommendations” and “looking forward to their continued guidance in this area.”

In addition to exploring humidor options – currently only used at hitter-happy ballparks in Phoenix and Denver – MLB said it will:

Make updates to the existing production specifications of baseballs and develop additional specifications for the aerodynamic properties of the ball.

Perform aerodynamic testing on baseballs

Create standards for “mud rubbing,” a process by which new balls are rubbed down by home teams using a specific mud from the New Jersey area.

Form a scientific advisory council.

In 2017, a record 6,105 home runs were hit, capping a significant leap in the home run rate that began around midseason 2015.