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‘Definitely noticing a difference’: Stats suggest impact of D-backs’ humidor

The Diamondbacks will debut 2018 with a humidor in an attempt to reduce home runs at Chase Field this season. (Photo by Katie Woo | Cronkite News)

It’s a running joke among baseball insiders that statistics tend not to matter in a season until Mike Trout takes over his rightful spot atop the Wins above Replacement (WAR) rankings.

Every year, like the sun rises in the east and the NBA Playoffs spark LeBron vs. Jordan debates, Trout will gain a stranglehold on the WAR rankings — a statistic that values a player’s overall contributions to a team — and never relinquish it. With about two months removed from Opening Day, guess what? Trout is leading the league with a 4.8 WAR, according to Fangraphs.

Sample size be damned, it’s time to evaluate one of the more meaningful innovations in Major League Baseball for 2018: the Diamondbacks’ institution of a humidor-controlled environment for the storage of baseballs.

In theory, humidified balls gain weight and are less elastic than ones stored in the dry Arizona climate. This lowers the coefficient of restitution on the balls, meaning that more energy is lost in the collision of bat and ball. Thus, home runs should decrease and strongly hit balls won’t travel as far.

Through the first 32 games played at Chase Field, the results have been evident. provides a park factors statistic, a way of comparing home run rates at different ballparks. Any number larger than 1.0 means the park favors the hitter. A number below 1.0 favors pitchers.

Between 2013-2017, Chase Field finished as one of the top-five most hitter-friendly environments in the league three times, with an average park factor of 1.103. Currently, Chase Field sits in 13th with a park factor of 0.988.

“I think you’re definitely noticing a difference,” said Diamondbacks utility man Daniel Descalso. “We’ve seen some balls that come off the bat well that don’t necessarily carry like we thought they would.”

To be fair to Chase Field, the Diamondbacks have been hitting well at home as of late. They scored nine, six, and six runs in their three-game homestand this past weekend against Miami. But digging deeper, it’s clear the hitting splits at home are considerable worse for many of their major contributors.

Paul Goldschmidt – yes, the same Paul Goldschmidt who has made five consecutive All-Star teams and won three Silver Slugger Awards – is hitting .160 at home compared to .257 away from Chase Field.

When talking about the humidor’s potential effect on his play at home, Goldschmidt seemed indifferent.

“I’m not sure what effect it’s having, but the biggest thing is it’s affecting both teams the same,” Goldschmidt said. “There’s not an advantage for one team.”

For the Diamondbacks, the effects have gone beyond basic hitting and slugging stats (which, for the record, slugging is also down 12.1 percent at Chase Field compared to the previous five seasons), but Statcast tracking numbers back up the effect the humidor is having on these games.

The best advanced numbers to measure humidor impact are exit velocity and the average distance of balls in play.

In the three previous seasons, the average exit velocity of balls in play was 88.21 mph. Although in 2018 that number has stayed relatively the same (88.11 mph), the average distance these balls have traveled has fallen substantially.

The average ball-in-play distance from the same three-year span was 181.57 feet. This year, that number has fallen to 168.89 feet, a 7 percent decrease.

“Maybe those balls that were sneaking out the last four years are not going to get out anymore, but that’s just something we’re going to have to get used to,” Descalso said. “Maybe start adapting more of an on-top, line-drive approach instead of having those balls get caught.”

Diamondbacks manager Torey Lovullo seemed intrigued by the humidor but told media he would not talk on its effects until halfway through the season, at the earliest.

“I want to get that information, but I want to make sure that I’ve got enough information before I start to make comments on it,” Lovullo said. “I know that something probably could show a trend, and I’ll be sure to give you some of my thoughts at the midway point.”

It may take years of data to fully understand how humidor will change baseball at Chase Field, but so far the effects seem to be playing out as intended. If similar results play out over a larger sample, it will be interesting to see how the Diamondbacks make adjustments to their roster and strategies in coming seasons.

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