Astros Offseason: Dexter Fowler and the Coors Field Effect

Garrett Ellwood

A question that is repeatedly being asked is "Was Dexter Fowler aided by the thin air in Denver?" I decided to research this question and see how players hit when they go to another team.

Since Coors Field became the home of the Colorado Rockies in 1995, it has become where a pitchers ERA goes to die. Because of the elevation in Denver there are fewer dense air particles than there would be at sea level. This aspect can cause two things.

First, a baseball will travel farther in thinner atmosphere. A baseball hit 400 feet at sea level in Minute Maid Park will travel 420 feet at Coors Field in Denver. The other effect is that a breaking ball will not break as much since there will be less friction added to the ball to cause it to break. Generally this is a great thing for hitters, but for pitchers a hanging curve ball that travels 20 more feet can be nightmare inducing.

In order to see a possible drop off in hitting production when a player has been traded, or leaves as a free agent, I put together a list of players from each position that had a minimum 1000 plate appearances as a member of the Rockies and 1000 plate appearances after they left Denver. After finding players that met this criteria, I looked at their Weighted On Base Average (wOBA) while with the Rockies, and after they left.

Coors Field After Coors Difference
C Joe Girardi 0.311 0.296 -0.015
1B Andres Galarraga 0.401 0.372 -0.029
2B Eric Young 0.354 0.328 -0.026
3B Vinny Castilla 0.371 0.308 -0.063
SS Walt Weiss 0.332 0.315 -0.017
RF Dante Bichette 0.371 0.348 -0.023
CF Ellis Burks 0.408 0.393 -0.015
LF Matt Holliday 0.400 0.388 -0.012

As you can see my search resulted in re-creating the mid-90's Blake Street Bombers plus Matt Holliday. Everybody declined in wOBA by an average of -.025 after changing teams, and it would seem likely that Fowler could also slightly decline after leaving Coors Field. His career wOBA is .349 and if you decrease this by the -.025 average, you could be looking at a player with a wOBA of .324, which is still not bad, considering the guy he is replacing in Center Field, Brandon Barnes, had a wOBA of .283, and last year Jason Castro (.361) and Chris Carter (.337) were the only Astros to outscore him according to this statistic.

Something to note with this would be that most of these players were already in the decline of their careers when they left, and that could also contribute in the decrease. Fowler will be in the prime of his career and maybe he could have very little drop off when leaving Coors field like Holliday.

The fan in me wanted the numbers to show something different than this, but hopefully his numbers don't drop as much as Vinny Castilla.

What are your thoughts?

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