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In late August, Red Sox manager Alex Cora elected to keep J.D. Martinez in the outfield for the ninth inning with a two-run lead on the road — a departure from a tactic he frequently employed in the previous year, when he often replaced Martinez with Jackie Bradley Jr. when Boston had a late lead. The Red Sox manager offered a succinct explanation as to why he was no longer using his 2018 game plan.

“Different year, bruh,” Cora posited.

Those three words spoke volumes about how, in recent years and including this postseason, an aspect of the game easily taken for granted has created uncertainty, change, and chaos throughout baseball.

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In an era where everything is measurable, there is clear evidence that the baseball — the most fundamental piece of equipment in the sport — has changed in critical ways. The home run explosion of recent years, which helped pull the sport from an offense-starved era, commenced in the middle of the 2015 season. Balls that had expired on warning tracks suddenly started finding their way into the seats with increased frequency.

Studies including tremendously illuminating work by Rob Arthur of Baseball Prospectus, as well as a report commissioned by MLB to study the home run surge found the culprit: Drag, or air resistance, on the flight of the baseball had decreased. The MLB committee could not identify an exact reason in the ball’s manufacture for the change in drag, but sports data scientist Meredith Wills subsequently found several potential elements in the construction of the ball that might impact its flight through the air.

Early this season, numerous studies acknowledged that drag had again decreased in significant fashion. The results during the 2019 season were jarring, as baseball destroyed its all-time home run record in a season during which every fly ball seemed destined to leave the park.

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The way the ball carried altered the game at the field level in fundamental ways. As Cora noted, managerial decisions were framed with an awareness that the threat of a homer was omnipresent. Wisdom from the Red Sox manager’s own playing days — that a two-run lead was surmountable with “a bloop and a blast” — had shifted to a fear that a walk and a relatively routine flyball might suffice to erase such an advantage. Different year, bruh, indeed.

For hitters, the reward calculus of an all-fields approach changed. Through most of baseball history — and particularly at the beginning of this decade — hitters needed to crush the ball to the pull side in order to leave the yard.

In 2019, Statcast identified an astonishing 1,093 opposite-field homers – a massive 62 percent increase from 2018, and a 160 percent increase from 2014. The ability to drive the ball out to the opposite field suggested an increase to the number of zones where hitters could attack pitches and drive them out of the park.

“I know that years back, hitting to the opposite field, it was almost like, ‘You want me to punch the ball over there, fillet it?’ ” Red Sox hitting coach Tim Hyers said during the season. “With the ball and some of the strength levels of the players, the ball carrying out of the ballpark, one thing I’m seeing more than usual is the opposite-field home run.”

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For pitchers, the notion of a good pitch changed. Certain safety zones disappeared if opposing hitters could manage to get to those pitches and lift them. Pitchers who made their living by commanding the ball in specific areas suddenly found their skill sets to be less valuable.

“One of our pitchers made a really good pitch in a really good location. It actually was above the zone, kind of in, and it ended up being hit out,” noted Twins chief baseball officer Derek Falvey during the season. “I was like, ‘Wow, you actually executed what you were trying to execute and the guy hit it out of the yard.’ ”

Such outcomes became commonplace during the season — yet have undergone another massive shift in the postseason. Arthur updated his findings about drag, and discovered that the ball was encountering more air resistance than at any time since at least 2016, meaning that games have been featuring a “dejuiced” ball.

Through Wednesday’s playoff games, Arthur found that the contact properties (exit velocity, launch angle, direction) of balls put in play during the postseason would have been predicted to result in 100 homers with the regular-season ball. Instead, just 64 of those had left the yard.

Cardinals manager Mike Shildt said during the NLCS that his team’s analysts found that fly balls were traveling an average of 4½ feet less during the playoffs than they had been during the regular season. Balls that had been landing in the seats were turning into outs, transforming how games were being played.

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In its own right, the changing properties of the ball don’t create unfairness. After all, both teams are employing the same set of baseballs. At the same time, players have found it jarring to see the conditions of the game changing radically — all while MLB says that it doesn’t know what’s happening to the balls, even though the league owns 25 percent of the company (Rawlings) that manufactures them.

Major League Baseball said the baseballs being used in the postseason came from the same batches that were manufactured for the regular season.

“I just think in a game that can be so different based on the ball that’s in play, we should definitely take some steps in normalizing it or having it be at least the same,” Astros pitcher Justin Verlander told reporters on Thursday. “Consistency I think is something that makes this game so special. When you look to compare numbers to greats a hundred years ago, it’s such a unique sport with the history that we have, and it’s been played on the same dimensions for so long. You start changing some of those things and one of the best parts of this game goes away.”

Moreover, the idea of in-season changes to the ball creates a potentially alarming challenge when it comes to evaluating players. A pitcher might find himself out of a job based on how the ball jumps off the bat in one season — only to see the value of his pitch mix skyrocket the next season due to a dejuiced ball. A hitter might receive a massive contract based on a power explosion in 2019 — before seeing his value dwindle for a new team if next year’s ball harbors more similarities to the postseason ball than the regular-season one.

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“If pitches move differently, if a certain pitch doesn’t work as well, or a certain pitch to a certain location doesn’t work as well, we’ve got to be ahead of that,” said Falvey. “That’s going to be a challenge. That’s going to be a challenge for all 30 [teams].”

The nature of the challenge appears larger and more bewildering than ever. It is now clear that the game is subject to massive changes based on the fact that the ball — assumed to be one of the game’s foundational constants — is in fact variable, in a way that has enormous implications for how the game is played and seen.


Alex Speier can be reached at alex.speier@globe.com. Follow him on twitter at @alexspeier.