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Is Chase Field No Longer a Hitters Ballpark ?

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What impacts are the humidor and new artificial turf having ?

For years Chase Field was known as a hitters ballpark, due to multiple factors. Thin, dry air; a great hitters background; a large outfield with some tricky corners; a typically closed up ballpark, with roof and panels shut for most games from early May through Mid-Late September (so no wind blowing in). All these combine to make Chase one of the more hitter friendly parks in the league.

This appears to have changed. We can’t tell for 100% certain, or just to what extent 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.

One might ask, why should I care? There are two primary reasons:

1.) Playing home games in hitters parks puts more wear and tear on your pitchers. They have to face more batters, and expend more pitches and energy to record outs, and over a long season, this adds up. Great pitchers are still great, and we’ve had our share at Chase Field. On the whole, playing in a hitters park adds stress and wear and tear to the staff.

2.) It’s important for player evaluation. Posting a 3.50 ERA in Petco park is merely average. Posting a 3.50 ERA in Coors Field puts you in the running for the Cy Young Award - or at least it should. Hitting .300 with 30 homers playing home games in San Francisco is REALLY hard to do. Doing the same in Arlington, Texas is much much easier.

So being able to contextualize player performance is vital to the evaluation process. And lets’s not kid ourselves. None of us are GM’s or making any decisions. But we all form opinions on players, at least in part, based on how we perceive their performance through their Statistics. So how do we better understand how to go about this?

We can see this by looking at a couple of resources that measure park factors and then create metrics that take those park factors into account. Most who read the pages of AZSnakepit are at least somewhat familiar with these. As a reminder, to keep things simple, the baseline of 100 is used, where 100 = average, and over 100 favors hitters, and under 100 favors pitchers. For context, the most hitter friendly park in the league, Coors Field, typically has a runs park factor anywhere from 125-150, (meaning it inflates run scoring anywhere from 25-50%!) and a components park factor, (i.e. OPS or wOBA, of 115-125). Some other very hitter friendly parks typically include The Ballpark in Arlington Texas, Great American Ballpark in Cincinnati, Fenway, and the new Yankee Stadium. But there is usually a pretty big gap between those parks and Coors. (Although Arlington sometimes actually pips Coors).

The most pitcher friendly parks, such as Petco, Safeco, AT&T, Citi Field & Dodger Stadium for example, typically have a Runs Park Factor of around 70-80, and a Components Park Factor of 80-90

It’s really important to note that all of the major stats sites that offer Park Adjusted stats, like OPS+, ERA+, ERA-, wRC+, etc, use Multi Year Park Factors. There is just too much fluctuation from one season to the next not to do so, but over a longer period of time, the true nature of a ballpark begins to emerge.

And so it’s been with Chase field. The below table breaks out 2009-2017, and shows the average, and then includes separate lines to see 2018 & 2019 YTD. (Note, I used the decimal point, so 1.00 = 100 in the park factor scale discussed above). The basic formula takes DBacks hitters home and road, and measures against Opponents numbers in Chase field and in DBacks road games. The Formula looks like this:

((homeRS + homeRA)/(homeG)) / ((roadRS + roadRA)/(roadG))

Here are the key takeaways you should be getting from the above table:

For the 9 year period from 2009-2017, Chase Field inflated run scoring about 13% and ranked on average as the 6th most friendly park for scoring runs. It inflated homers and hits, and especially double and triples. The HR park factor of 110 is fairly consistent.

There are outlier seasons. 2013 in particular played slightly pitcher friendly. 2015 was not a homer friendly year, but extra base hits were plentiful, and made up for the lack of HR.

If you take out 2013, the Average runs ranking becomes 4.5. So it’s no stretch to say that Chase Field was a top 5 hitters park in MLB in most years by most measures.

Then two things happened. The first was in 2018 the team introduced the Humidor. Visually, it seemed to have an effect in shortening up fly balls and reducing HR at Chase. We can see the HR factor dropped to 96. But there existed those 2013 and 2015 seasons, so we couldn’t be sure it was really the humidor. As I said, there is plenty of fluctuation in these numbers. However through 43 games so far this year, (20 at Chase, 23 on the road), the HR factor has dropped further to 89. So it appears that the reduction in HR could be here to stay. That number can move quickly mind you, especially this early in the season. But it appears safe to say that relative to the league, Chase field is no longer a HR friendly park. At the very least, it’s probably neutral and no longer favors hitters.

The Runs factor for 2018 was also lower than the previous 9 year average, but it could have been an outlier season perhaps, just like 2013.

But now, just look at 2019 !!!

The numbers are showing Chase Field as a PITCHERS PARK YEAR TO DATE. The sample size is small. However look not just at Runs (0.82 , ranking 24th!) and HR, but also Hits, Doubles, and Triples. These numbers are all well below previous levels, even 2018 Humidor season. What’s up here ?

I think it’s the artificial turf. It plays slow. Real slow. Chase Field always had a hard fast infield. And so it always inflated hits on groundballs, (BABIP, or Batting Avg on Balls in Play), and ALSO helped to inflate Doubles and Triples, as the ball would take off and scoot through gaps and into the corners. However anyone who goes to a lot of games at Chase can see that the new turf plays slower. Players and coaches have mentioned this too. And the data is showing it , emphatically:

So what you can see is that Batting Avg on Ground balls was about 3% higher than league average over a 9 year period, and was actually 6% higher in 2018, despite the humidor. But so far in 2019, it’s 9% LOWER.

This is a big deal. As I said, not only is the new turf reducing hits, but it’s also potentially reducing doubles and triples, which as mentioned above, have also been sharply reduced.

The goal of the team may have been to make Chase Field a neutral ballpark. However it’s very possible that Chase Field is now a PITCHERS BALLPARK. I’m not sure if the front office is happy about that or not.

And here is one more thing. Remember I mention that Baseball-Reference, Fangraphs, etc all use multi year park factors to calculate their park adjusted metrics. Well that means they are potentially way behind the curve in adjusting things like ERA+, OPS+, etc. It means those metrics would be overrating the pitching and underrating the hitting.

Here is one simple example:

Baseball Reference has a single year park factor of 90. However the Multi year park factor is still at 105, as it takes a long time for the current year to have an impact. BR uses the year prior, the current year, and the year after. So for example the multi year factor for 2017 would be using 2016, 2017, and 2018. (ttl of 107+113+104. / 3 = 108) But while the current year is being played, there IS no next year, and the current year is only partial and has to be prorated to effect the previous year....until the year is over. I know that’s a little confusing, perhaps seeing it in Chart form below will help


Year Multi PPF Multi PPF 1 yr PPF 1 yr BPF
Year Multi PPF Multi PPF 1 yr PPF 1 yr BPF
2019 104 105 90 89
2018 105 106 104 103
2017 108 108 113 112
2016 107 107 107 108
2015 105 105 103 103
2014 102 102 104 105
2013 103 102 99 100
2012 103 103 104 104
2011 103 103 107 106
2010 105 105 98 99
2009 106 105 110 110
2008 107 107 108 107
2007 107 107 105 105
2006 105 105 107 107
2005 104 103 102 103
2004 106 105 101 104
2003 109 108 113 113
2002 110 111 110 109
2001 107 108 111 110
2000 103 104 104 103
1999 100 101 100 98
1998 99 100 100 101

So there is a pretty big lag. Most won’t notice, but BR Park Adjusted metrics actually change retroactively once the following year is complete. For some this is bothersome, but for me it’s fine. It just means it takes more time to have an accurate reading. HOWEVER, it does create challenges when evaluating players in the present. Just how good is a 3.14 ERA for a pitcher pitching in Chase this year? The 140 ERA+ that Zack Greinke, Robbie Ray, and Luke Weaver all have at the moment would probably be 125 if the current year park factor were applied instead of the multi year. How good is that .900 OPS? Maybe a lot better than we think. David Peralta’s 132 OPS+ might end up looking like a 145 OPS+ if the current park factor number holds true. Those are pretty big differences.

One final note. From a fan enjoyment perspective, I love that the new turf allows the team to keep the stadium closed up and cool all day and then open the roof at night even when it’s high 90’s to low 100’s. The experience is just so much better. By the end of this year, the number of games with Roof and Panels open will probably double from previous years. And for that alone, we should be grateful.


ESPN Park Factors

Fangraphs Park Factors

Baseball-Reference Multi Year

DBacks BR Home Page

DBacks Franchise Index Attendance and Parks Page