Where have all the home runs gone in MLB postseason games?

Just before the playoffs started a rumor dropped on my Twitter timeline that Major League Baseball was considering changing the balls for the postseason. It was not from an authorized account, but the sources they noted seemed more plausible than a lot of the utter nonsense I see on Twitter. So I retweeted it and made a mental note to keep an eye on home run rates during the postseason:

I’ve thought about this tweet a few times throughout the postseason, but notably as balls that I remember just rocketing out of ballparks earlier in the season died on the warning track. Like this ball that had all of Atlanta and St. Louis debating Ronald Acuña Jr. and his hustle or respect for the game or whatever [VIDEO].

My hunch was that home run rates were down, but I couldn’t prove it and didn’t have access to the right data sets to crunch the numbers. So I’ve just been keeping an eye out for information. Well, this morning Baseball Prospectus published exactly what I’ve been looking for in this bombshell piece from Robert Arthur (emphasis added):

In the past, manufacturing variation was a believable explanation. After all, producing baseballs is a complex, multistep process, involving many different organic components and some manual steps. It seemed plausible that, from year to year, minor variations in the machines, materials, or even in the pool of poorly-compensated Costa Rican laborers who assemble the final product could contribute to slight differences in drag and thus home runs. That fit with data that showed only small alterations in drag from month to month or week to week, with much larger spikes and drops in drag from the end of one season to the beginning of the next (when lots of changes to the assembly line would presumably take place).

But this change is very different. Almost overnight within the same season, the ball has been replaced by one with wholly distinct characteristics, ranging from the speed with which it leaves the bat to the distance it travels. It’s hard to believe that MLB, which owns the company that produces the baseballs, would consciously approve a change to their manufacturing on the eve of the most important month of the season, but it’s also hard to believe that this would happen by accident.

Your eyes are not fooling you, the ball is different, very different and it happened just in time for the postseason. I encourage you to read the whole article but this chart tells the story as succinctly as it can possibly be told:

Robert Arthur/Baseball Prospectus

Arthur tracks the drag coefficient of the baseball throughout the season. It’s how he knew the ball was different in 2016, and knew it was different again in 2017. It’s something he started watching in earnest in 2019 as home run records fell all over baseball. But that spike of on the drag coefficient for the playoffs is really something else: It’s the first evidence of a juiced ball effect that was potentially orchestrated for a specific time. As Arthur hypothesize:

MLB certainly had reason to want fewer dingers in the postseason. More homers and offense means longer games, especially with the cavalcade of pitching changes that arrive in October, and that could spell reduced audiences. And as Ben Lindbergh wrote in an article at the Ringer, the prospect of a random, weakly-hit fly ball meandering over the fence (as so many did throughout the year) and deciding a crucial series could have been embarrassing for the game.

Instead, baseball’s audiences are left in the opposite position: wondering why a pitch that Muncy pulverized only made it five feet shy of the fence when so many similar hits left the park. Whether intentional or accidental, changes to the baseball appear to have shaken up the game again–and this time at the most crucial and decisive point in the season.

His conclusion is the part of this that is so beyond aggravating to me as a baseball fan. What exactly is the point of playing a 162-game season to see who the best team is in a given year if the most fundamental piece of equipment is altered for the playoffs? How might any team’s season have been different with non-juiced balls in the regular season, or juiced balls in the playoffs? We will never know the answer to that, but it’s a haunting question for pitchers who gave up inexplicable home runs on balls that have always been long outs, or for players who thought they’d hit a walk off in the division series only to come up bafflingly short.

The Commissioner’s office needs to be substantially more transparent about its decisions surrounding the physical ball going forward. There should be clear parameters and protocols for any announced changes. Given the effects that juiced balls can have on player stats and performance, the next Collective Bargaining Agreement should likely include terms for disclosing any changes in manufacturing to teams and players. It’s unacceptable to deliberately alter the ball for the postseason, but to do so in such an opaque way is a substantially larger threat to the health of the game than a four hour slug fest would have been.