What has been speculated for years was finally made official Tuesday night when Diamondbacks general manager announced that the club would use a humidor to store baseballs before use in Chase Field this upcoming season (via azcentral.com).
Without getting too far into science here, humidors absorb moisture and make the baseballs a bit "heavier" in terms of their bounce. That is, they won't be hit as hard. There is one example in MLB where a humidor was introduced and the results showed the impact on offense.
Now, Coors Field is obviously still the best hitters park in baseball, but it was outrageously more drastic before the humidor was introduced before the 2002 season.
In 1999, there were 1,198 runs scored in Coors. No other ballpark saw more than 963 (then-Jacobs Field). In 2000, Coors topped the majors with 1,164 runs while then-Enron Field was second with 1,005. In 2001, Coors saw 1,085 runs while no other park topped Ballpark at Arlington's 939. Kauffman Stadium checked in at third with 867.
Those are amazing gaps.
Coors Field still had the most runs in 2002, but it fell to 989 with Ballpark at Arlington sitting at 957 and Kauffman at 939. In 2003, Coors Field didn't lead in runs. Ballpark at Arlington saw 985 with Coors at 967 and Kauffman at 945. Fenway Park witnessed 927 with Toronto's then-Skydome also topping 900. There was a jump for Coors in 2004, but in 2005, it fell below 900 runs with Great American Ball Park taking top honors.
Here's a look at the rate stats in the three years before the humidor and then the two after compared to league average. Remember, there's an imaginary line between 2001 and 2002, because that's when the Rockies started to use the humidor.
Taken along with the runs scored changed that I noted above, Major League Baseball saw Coors Field come from a veritable slow-pitch softball setting to simply one of the best hitters parks. The latter is fine, but the former was getting to the point of making a mockery of the game.
As for Chase Field, by no means has it even remotely been a problem. No, the discussion that's important here is what exactly the humidor will do to the way the ballpark plays. It's known as a hitter-friendly yard. It ranked eighth in MLB in runs last season behind Coors, Rangers Ballpark, Comerica Park, Target Field, Oakland Coliseum, Great American Ball Park and Wrigley Field. It ranked 11th in home runs.
The league average slash was 2.55/.324/.426 while the Chase Field slash was .256/.327/.449 with a 106 OPS+.
Basically, it was hitter-friendly, but not drastically so. Mildly, perhaps.
Given what we know about the humidor affect on baseballs in Coors Field, it's reasonable to believe the humidor transforms Chase Field into a pitcher-friendly park. In fact, The Hardball Times published a study from a University of Illinois physics professor on what effects a Chase Field humidor would have. He estimates there will be a reduction in home runs in Chase Field by a whopping 25 to even 50(!) percent.
The Diamondbacks collectively hit .274/.350/.492 with 122 home runs at home last season vs. .235/.309/.398 with 98 homers on the road. Obviously, pretty much every team hits better at home than on the road due to comfort reasons, but that's a big split.
As for the other side, expect Arizona pitchers to fare much better now. They had a 3.79 ERA with 93 home runs allowed in Chase Field vs. 3.55 with 78 allowed HR on the road.
Overall, the D-Backs were fourth in the NL in runs, fifth in home runs, second in slugging and fourth in OPS. They were second in the NL in team ERA while only the Indians coughed up fewer home runs in all of baseball. If the humidor does what it's expected to do, the D-Backs are looking at a potentially-dominant pitching staff while regressing on offense. Maybe it'll even out in wins and losses and simply look like a different type of winning ballclub.
This is a storyline definitely worth keeping an eye on this season in Arizona.