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The Curious Case of the Chase Field Humidor

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More than seven months ago, “finishing touches” were being applied. Now? Not so much...

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World Series: Boston Red Sox v Colorado Rockies - Game 3 Photo by Rich Pilling/MLB Photos via Getty Images

The idea of a humidor at Chase Field has been kicked around for a long time. The park has always had a reputation as one of the more hitter-friendly in baseball. It’s the second-highest in altitude, behind Coors Field, and the lack of humidity in the desert arguably makes the non-altitude conditions in Phoenix have a greater impact than in Denver. The Rockies have used a humidor since 2002, to help reduced the impact of the environment, and it certainly had a significant effect, reducing home-runs by about 22%. Ways to make Chase Field less hitter-friendly have been explored since at least 2010, including not only a humidor, but also changes to the park’s dimensions.

Nothing came of this until last April. The previous season, the D-backs’ pitching staff had stumbled to a 5.09 ERA, the very worst in the National League, and this may have played into the decision. Team president Derrick Hall said the aim was to improve grip on the mound, “We talked to former pitchers, whether it’s J.J. Putz or pitchers who have retired or pitchers we’ve traded, and said ‘what did you like, what didn’t you like?’ They all talk about the grip. The one thing you don’t really want to do is negatively impact the offense, because that’s part of the fun of Chase Field or Coors Field, but I don’t think it really did diminish the offense at Coors Field. We don’t know if it’s going to make much of a difference, but it’s probably a necessity.”

At the time, it was said that construction of the necessary facility in the bowels of Chase Field “should take about another four to six weeks,” with additional time for testing. Balls then needed to be stored for two weeks in the humidor before they could be used in a game. Initially, things seemed to be proceeding on track. A June 24 report stated it was “almost fully operational,” adding that “there had been tentative plans for the humidor to be up and running this weekend.” However, GM Mike Hazen said it would not be in use until “somewhere around or after the All-Star break.”

But just five days later, it was announced that the “almost fully operational” facility now would not actually be in use for any part of the 2017 season. MLB spokesman Michael Teevan said, “Given that the approval came in March, the timeline of the project was different than projected. Now we’re almost into July. I think the concern was, to change it midstream, it was not something people were entirely comfortable with.” That does kinda makes sense: the story went on to say the team would “wait until the offseason to put the finishing touches on the humidor...with the hopes of having it fully operational by the start of next season.”

That was seven months ago. Given the nearly-complete state of the facility in June, I would have expected things to have been completed in short order, with plenty of time to get all the necessary testing completed as well. Which made this Tweet last Tuesday from the Diamondbacks all the more surprising:

Of course, this could be entirely innocuous: the process might simply have been on the back-burner, and there is still plenty of time for everything to be completed over the two months between now and Opening Day. But the team has been notably reticent about the whole thing: the June 24 article noted “Since it was learned in April that the Diamondbacks were adding a humidor, team officials have been reluctant to talk about it publicly, at least in any detail.” I would not be surprised at all if there has been a change in heart - not least because gripping the ball appeared to pose no problems at all for the 2017 staff, whose ERA of 3.66 improved from 15th to 2nd in the league.

In theory, you’d think a humidor would depress runs scored and allowed by an equal percentage, and have no overall impact on a team’s Pythagorean (expected) record. But I’m pretty sure the front-office have dug into the numbers a great deal deeper. Perhaps (and this is speculation) they’ve found data to indicate it would hurt our hitters more than it would help our pitchers. That might make sense: the curve for a top-tier pitching staff like Arizona’s to improve would be significantly steeper. The further you get from average, the tighter the elastic of regression pulls you back [it’s easier for an 80-win team to improve by ten wins, than a 100-win team].

It is certainly possible that a humidor would not affect all players equally. Most obviously, fly-ball pitchers would presumably see a greater impact, with balls that were previously leaving the park now falling short. But the team likely has StatCast data for every ball in play at Chase Field last season, and can use that, along with the work of people such as Professor Alan Nathan, to figure out exactly what would have happened to each of them, had the ball been humidored humidorified in a state of humidorification kept in a humidor, dammit. The math will presumably have been done, and if it shows a negative effect on the team, might explain the silence regarding it.

Of course, I may be entirely wrong with this, and the humidor could be in full effect by the time the first pitch is thrown in April. But if it isn’t, and the idea is quietly dropped by the Diamondbacks... Well, you heard it here first!