Chase Field Played as a Neutral Ballpark in 2019

Back on May 15th I published an article Is Chase Field No Longer a Hitters Ballpark? I would like to suggest you go back and review that article quickly.

Still here? No really, please go take a look, as it will make it easier to understand what is below.

In the 2nd paragraph of that May article I wrote:

We can’t tell for 100% certain, or just to what extent (that it’s no longer a hitters’ park) just yet. In the world of numbers, this sample size is still not quite large enough to be able to say Chase is no longer a hitters park with absolute conviction. But personally, I’m getting pretty darn close to saying that.

So I’ve been tracking this throughout the season and several times was about to write an update. Through the first half, the numbers heavily favored a pitchers’ park result, not just neutral. But then about mid season, I noticed the numbers start to move. The team started hitting better at home, and things slowly started to level out. I kept holding off doing the update; I’m glad I did and gave the numbers time to settle. So lets go one by one and look.

Starting with home-runs, we saw last year that the Humidor had an impact on home-runs at Chase Field. While MLB smashed HR records this year, and HR at Chase were up from last year, in fact relative to the rest of the league the HR Park Factor went down, i.e. LESS homer friendly than ever. In 2019 the .89 HR factor ranked 20th in MLB. The 2018 Factor of .96 ranked 19th. So if you hear one of your friends say that Chase is a “launching pad”, you can say with confidence that it no longer is. We now have two years of data with the Humidor that pretty clearly shows HR have been brought in line. (If you went back and reviewed the previous article, you know that a factor less than 1 favors pitchers, and over 1 favors hitters)

*Note in the above table I show the HR factor at various points in the season. Those are HR percentages, as the number of games played home and away was not even at those interim points. The Factor on the right is the key. You can see the factor moved from .828 to .89 since August 8th.

The second piece of this is Groundballs/Turf. And here something really surprising (to me) happened. Throughout the first half, the numbers indicated the new turf may be playing slower than before, as base hits on ground balls were greatly reduced. . However over the 2nd half, that changed rapidly, and by the end of the year, they came in line with previous seasons. Someone, I can’t remember who, had pointed out that they had read that over time the field would start to play a little faster, as the infill settled in. Whatever the reason, the end of year numbers say NO CHANGE from the 10 year average, and just a little less hit friendly than 2018. Once again note the progression at the various points I recorded throughout the season

Here is the overview with all categories together, including wOBA which I added. As you can see, the runs rank - which is ultimately what we are most interested in - the average for the 10 year period 2009-2017 was 6th. It fell to 11th last year, and was 16th this year. Any way you slice it, that’s pretty much neutral relative to the rest of MLB. The park is still very triples friendly, due to the corners and configurations. That makes up for a little bit of the HR reduction.

Finally, here is one last indicator. Baseball Reference has their park factors as well. You can read about how they calculate them HERE. Warning, NSFMP. (Not suitable for Math Phobes)

But if you go to the D-backs Home Page or any team for that matter, you will see near the top in the team info section the Single Year and Multi Year Park Factor. The multi year being based on the current year, the year prior, and the year after. Obviously the year after 2019 hasn’t happened yet. But once it does, the 2019 factor will be adjusted accordingly. This is notable because for example heading into 2019, the 2018 Multi year park factor was 109. But after this year, it’s been lowered to 105. That impacts all park adjusted metrics such as OPS+, ERA+, and WAR retroactively.

As you can see, back in 2010 and 2013 there were in fact seasons with similar single year results. So it’s always possible that the 2019 result of 99 is subject to change next year. (Remember 100 = Neutral, so 99 slightly favors pitchers, as does the ESPN result of .98 Runs where 1.00 = Neutral)

This is why BR uses multi year factors: they are less subject to wild swings. When changes do show up, they are more gradual. However the main difference the last couple of years is of course the humidor, and the new turf. Another potential factor is more games with the roof open, since the new turf allows for that. But I can’t split out home games with roof open vs. closed, compared to previous years.

I’m confident the changes the team has made has created a more neutral run environment at Chase Field. This is better for pitching, because when the run environment is very high, it puts a lot of extra wear and tear on your pitching staff. Furthermore, when it comes to evaluating players, in the past it was easy to overrate hitters and underrate pitchers, as raw stats that erre not adjusted for ballpark environment get distorted. Chase was never as extreme as Coors Gield of course, but it was consistently among the more hitter friendly parks in the league. Kudos to the team for creating a more neutral environment.