Just as the Rockies have been doing for years in Coors Field, the Arizona Diamondbacks have started using a humidor to store their baseballs this season. Heading into the season, there was much discussion about the impact the humidor might have. I discussed it back in February and expected the offense in Chase Field to be suppressed compared to how it's been in the past.
The impact of a humidor on the baseball is it absorbs moisture and makes baseballs "heavier," meaning players don't hit the ball as hard as they would on non-humidor baseballs. The expectation heading into this season was that the humidor would transform Chase Field from a hitter's park into a pitcher's park.
Now, we won't fully know the impact until we have years worth of data, but let's still check in on how much impact there might have been so far. The D-Backs have played 24 home games entering Tuesday night. That's a decent sample, but obviously still relatively small compared to the 81 they'll play there all season. As such, small-sample caveats apply.
In 2017, Chase Field saw 803 runs scored. That's an average of 9.91 runs per game. That ranked eighth in MLB. The park ranked 11th in MLB in home runs with 215, an average of 2.65 per game. Here's the slash line versus the league average.
2017 Chase Field: .256/.327/.449; 106 OPS+
2017 MLB average: .255/.324/.426; 100 OPS+
It was a hitter-friendly park, but not significantly so.
Thus far in 2018, Chase Field has seen 164 runs and that's an average of 6.83 runs per game. There have been 44 home runs, an average of 1.83 per game. Small sample, sure, but that's a huge drop from the 9.91 runs per game last season. The slash versus league average ...
2018 Chase Field: .215/.289/.360; 79 OPS+
2018 MLB average: .246/.319/.407; 100 OPS+
Yikes. Offense is way down in Chase Field. As most everyone knows, teams generally hit better at home than on the road, unless there are extreme cases of pitcher-friendly ballparks. Is Chase Field now in that territory? Check this out, the Diamondbacks' slash lines at home versus on the road so far this season.
D-Backs at home: .217/.299/.355; 80 OPS+
D-Backs on road: .233/.308/.429; 102 OPS+
Contrast this with last season.
2017 D-Backs at home: .274/.350/.492; 118 OPS+
2017 D-Backs on road: .235/.309/.398; 93 OPS+
It's been a complete 180.
We obviously can't be 100 percent sure this is all the humidor, but it has certainly impacted the offensive side of things. There's too much evidence that says the humidor matters. As the season continues, perhaps things will change. Again, it's still relatively early. It's only 24 games out of 81. So far, though, it looks like the humidor is having a significant impact in Arizona. It's fair to say Chase Field is well on its way to being known as a pitcher-friendly yard.