How the humidor will impact the Diamondbacks' hitters and pitchers

A.J. Pollock, Jake Lamb and Paul Goldschmidt will all be impacted by the addition of the Humidor at Chase Field. Jake Roth-USA TODAY Sports

Finally, something to talk about other than Shohei Ohtani.

Last summer, the Arizona Diamondbacks put fantasy baseball on high alert, unveiling plans to install a humidor in Chase Field. Issues with calibrations delayed the launch to the point Major League Baseball told the club to put if off to the 2018 season. Over the winter, news whether it was still a go was sparse, with only a tweet suggesting we'd find out closer to the season. Part of the holdup was the Snakes were talking with their landlord, Maricopa County, about park renovations, with the threat of leaving for a new venue.

On Tuesday, it was finally revealed: The Chase Field humidor is a thing. Beginning this season, game balls will have been stored in the humidor, adding moisture to the cowhide, ostensibly to improve the pitcher's grip, but in fact the repercussions will extend well beyond that.

Baseballs dry out in the hot, arid desert air, rendering a slicker covering. The Diamondbacks will store the game balls in a humidor at the MLB-recommended 70 degrees with 50 percent humidity, yielding balls akin to those used at other ballparks.

Back in 2002, the Colorado Rockies became the first squad to utilize a humidor. Club officials noted the balls used at Coors Field were lighter and smaller than MLB specifications, suggesting the dry air, along with the reduced pressure, dries them out. Balls already travel more in the mile-high thin air, so the hope was not only for improved grip but also that a slightly heavier, larger ball would carry less in home games.

Unfortunately, although it is counterintuitive, a slightly heavier ball travels farther than a drier one. So why has run scoring sharply declined in Coors Field? In 2008, Edmund R. Meyer and John L. Bohn, a pair of University of Colorado, Boulder physicists, published "Influence of a humidor on the aerodynamics of baseballs," concluding the elasticity as measured by the coefficient of restitution lessens on denser balls, reducing flight.

Fast-forward to 2017, and noted physicist Alan Nathan wrote "A Humidor at Chase Field: What's Up With That?" after the Diamondbacks announced their intentions. In this, Nathan revisited previous work published in 2011, corroborating those findings using Statcast data. Speaking in current parlance, Nathan determined using humidor-stored balls drops the mean exit velocity 2 mph. Further, he concluded homers should decline 25 to 50 percent in Chase Field.

Such a huge drop sent shock waves throughout fantasy baseball. How will this affect Arizona hitters and pitchers? Where should they be ranked?

A reduction in home runs is only part of the puzzle. Lowered exit velocity influences all batted balls. The better grip could lead to more whiffs and fewer walks. With respect to pitching, the challenge is deciphering how Chase Field will play in terms of runs.

There will no doubt be in-depth studies using Statcast data, simulating how Chase Field will play going forward. The problem is a rare few have access to the information and the acumen to crunch the numbers. Besides, draft season is rapidly approaching. For some of us, it has already begun and "keeper" decisions need to be made. Offseason trading is in full force. Fantasy players don't want to wait; they want answers now.

The following method uses the concept of expected earned run average (xERA). There are many versions of xERA, some of the more common being FIP, xFIP and SIERA. The notion is a pitcher's ERA might not be reflective of his true skill level. In layman's terms, xERA fleshes out the luck, yielding what should have happened based strictly on the hurler's skills.

The first example of xERA was the brainchild of statistician Dwight Gill and sportswriter Tad Reeve. They devised an algorithm using hits, walks, strikeouts and homers. It's archaic in today's landscape but suffices to generate a usable runs park index for Chase Field.

The math is straightforward. Adjusted variables are plugged in, generating the number of runs that should be scored under those conditions. That total is then compared to the corresponding number of runs in road games to yield the runs index.

The adjusted number of homers is dictated by Nathan's research. Granted, it's a substantial range, but middling to 37.5 percent is a reasonable starting point. Research conducted on Coors Field, the only other case study, suggests reduced exit velocity cuts down hits by about 5 percent.

It's unclear how to tweak strikeouts and free passes. One of the effects at Coors Field thin air not felt in Chase Field is the reduced break on pitches. In both instances, better grip means increased spin rate and more movement on some offerings. However, the change won't be the same. Phoenix might have the second-highest elevation among MLB cities, but it pales in comparison to Denver. At least initially, the totals for punchouts and bases on balls will remain unchanged in the Gill-Reeve algorithm.

Looking at the previous three years, the normal span for park factors, Chase Field drops from 116 to 100. That is, without the humidor, the venue projects to inflate runs by 16 percent over a neutral park. With the humidor, it portends to play neutral.

Recalling this is based on a 25-50 percent range in home run loss and 5 percent fewer hits, seeing what happens with best- and worst-case scenarios provides a range of likely outcomes. Applying the maximum home run effect along with increasing strikeouts while shaving off some walks results in a factor of 95, a moderate pitchers' park. Using the minimum influence with a smaller decrease in hits while leaving strikeouts and walks the same results in an index of 105. Admittedly, this is a large range, adding another layer of risk-reward to drafting Diamondbacks pitchers.

Adding to the haze is Chase Field is already one of the more inconsistent venues. Beginning with last season's index, the factors for the past five seasons are 120, 122, 106, 116 and 97. The standard deviation for Chase Field's run index is one of the largest in MLB.

This method isn't perfect. It ignores that you can't just erase a homer and everything else would have stayed the same. There's a series of events affecting game flow. Was that lost homer turned into an out or a double? If it was still a hit, what would have ensued, keeping in mind most pitchers' skills are poorer from the stretch. An out versus a hit modifies the pitch count. Plus, this is only homers. What would the flow have been with different outcomes on other batted balls? Still, it's better than ignoring the impact.

Now that some parameters have been set, let's look at specific players and how their outlook changes. It's important to reiterate the range of outcomes is even wider than normal. Player expectation should always be thought of in terms of a range. The difference is now, until we get a better handle on post-humidor Chase Field, the error bar associated with Arizona players lengthens.


In the big picture, plan on Arizona batters losing hits and homers, piggybacked by a drop in runs and RBIs. The change won't be felt equally but no one is immune; they'll all suffer. Even Chuck Norris' exit velocity would drop with the humidor. The silver lining could be an increase in steals, as lower scoring is usually a harbinger for increased running. Even in a still run-friendly Coors Field, pilfers increased after the installation of the humidor.

Paul Goldschmidt

There's already some backlash on the perennial first-rounder. The laws of physics will not cease to exist on his bat. A 30-HR hitter should be expected to see a reduction by five or six. A .300 hitter expects to lose about .007 points. Runs plus RBI look to drop by 15 or so. In most draft leagues, Goldschmidt drops about 10 spots, going from a top-five pick to a late first/early second-round player. In auctions, he loses around $5.

Some are citing Goldschmidt's recent home/away splits, saying he has bopped only 25 of his 60 long balls the past two campaigns at home. This overlooks 2015, when he smashed seven more homers at home, narrowing the gap to just plus-three on the road. The point is, park factors should be applied ignoring splits of this nature. Even in a full season, there's too much noise.

Jake Lamb

Like Goldschmidt, Lamb lines up to lose around five big flies. He shouldn't lose as many points in batting average, but he'll still drop. Here's where he differs from his star teammate in terms of rankings. As you progress down the picks of a draft, the difference in potential between adjacent players is largest at the top, decreasing between consecutive picks throughout the draft. The best analogy is the NFL draft. A first and a fourth for a second and third is not an even trade. In fact, the league office sends each team a matrix, showing the expected value of each pick so deals can be fair. The repercussion for Lamb is even though he loses only $4 of projected value, $1 less than Goldschmidt, he drops over 50 places in drafts.

A.J. Pollock

Putting aside Pollock's penchant for visiting the disabled list, if the science comes to fruition, he stands to run a little more. In his favor is manager Torey Lovullo isn't shy about giving the green light. Last season, the Snakes slithered to the seventh-most steals in the league. Pinging Pollock elsewhere while adding five steals drops him only about $1, equating to 10 draft spots. Of course, the injury risk matters, but Pollock could be a discounted source for speed.

Ketel Marte

Marte isn't on the shallower mixed league radar, but he makes for an interesting point. The batting average on balls in play (BABIP) of hard-hit balls exceeds that of soft-hit balls. However, when medium is added to the classifications, it turns out the BABIP of soft-hit balls is higher than medium. This might seem counterintuitive, but a medium-hit grounder is most likely to be fielded cleanly without most runners able to beat it out. Also, a medium-hit fly ball is what old-school fans call a can of corn. Softly hit flies can fall in safely.

This is relevant since the majority of Marte's contact is of the medium variety. The possibility exists he'll actually gain some hits. If Lovullo wants to play more small ball, Marte stands to benefit.


The Diamondbacks already have one of the more intriguing staffs. Mix in a neutral ballyard and things get even more interesting. There's a notion a ground ball pitcher won't benefit as much as his fly ball counterpart, citing the difference in homers. While that's true, a ground ball hurler should have his hits reduced more than a fly ball guy. The elephant in the room is the effect on strikeouts and walks. While they didn't change the run factor appreciably, on an individual basis, fewer walks drops WHIP while more strikeouts obviously add to the fantasy value.

Zack Greinke

Given ERA is highly variable, Greinke lines up as a top-15 starter to as high as sixth, depending how you rank the highly skilled but injury risk options like Noah Syndergaard and Stephen Strasburg.

Robbie Ray

Ray is already a star in points leagues; now he's elite. He's an intriguing player on a granular basis. He has the unique ability to limit contact yet what he allows is among the league leaders in hard contact. You'd think missing so many bats would render more soft contact. If this trend holds, and the previous hard contact drops, Ray's hits could fall even more than others. The problem is, Ray is already a fantasy darling, so the potential profit is limited since his market price was already to the point there was little, if any, potential return on investment.

Zack Godley

With a ground ball rate routinely north of 50 percent, Godley is the specific arm some feel won't enjoy the same benefits of the humidor. He will, availing a buying opportunity. Godley is due some regression from last season, but the humidor will soften the blow. He should gain about 20 spots among starting pitchers.

Taijuan Walker

Walker's health is always a concern, but the humidor makes him a risk worth taking. He also picks up around 20 spots in starting pitcher rankings.

Patrick Corbin

Many benefited from Corbin's stellar second half last season. Some are anticipating a carryover, while others are more skeptical. When the market is divided like that, supply and demand economics dictate a more favorable price. With the humidor, the demand, hence the cost, elevates.


The Diamondbacks say they'll use the spring to decide between Archie Bradley, Brad Boxberger and Yoshihisa Hirano. Bradley has the best skills, but he also has proved effective in the ever-popular multiple-inning role. With the humidor, Boxberger's control and gopheritis might not be as much of a problem while Hirano's low strikeout rate won't matter as much. It's still anyone's guess, but those expecting Bradley to be the closer should be less confident.

Divisional opponents

With nine or 10 desert games, the other teams in the NL West will be affected. Keeping in mind a strong offense will still score runs in pitchers' parks, it appears only Coors Field will be off-limits for streaming. This makes the back-end starters on the Dodgers, Rockies, Padres and Giants more palatable, especially in leagues with daily moves. On the flip side, lower-end hitters from these clubs are less attractive, since there'll be many road trips with all neutral or pitchers' parks.