Setting Offensive Expectations Using Park Factors

Since it opened in 2004, Citizens Bank Park has had a reputation as one of baseball’s easiest parks to hit a homer in. Over the course of the last few years, data has emerged that other parks have overtaken CBP as more hitter-friendly parks.

A recent article by Baseball America’s Matt Eddy provided this handy graph that shows CBP’s place among other Major League parks in terms of runs and home runs per game:

As you can see, CBP ranks ninth-lowest in the Majors in runs per game while ranking fifth-lowest among National League teams. Eyeballing it, Eddy has the Phillies somewhere in the middle of the pack in home run rates, with eight teams clearly ahead of them on the graph while ESPN ranks them sixth in the Majors.

Eddy’s data suggests that the most common narrative, that Citizens Bank Park is a hitter’s ballpark, isn’t not necessarily true, or fully supported by data. Many others have written about this before and Eddy’s data isn’t anything revolutionary but his minor league data is something that I saw for the first time today.

In Eddy’s analysis, a park factor of 100 is around league average. As explained in the article, Eddy calculated minor league factors in this way:

The park factor (PF) column takes the ratio of runs scored and allowed at home and compares it with the same rates on the road and expresses it as an index, where 100 is exactly average. A park factor of 119, as is the case with Triple-A Charlotte, indicates that Knights home games featured 19 percent more runs than Knights road games in 2014. On the other hand, Triple-A Pawtucket, with it’s 79 park factor, scored and allowed 21 percent fewer runs at home.

As many Phillies’ minor league fans can tell you, the IronPigs, with their high fences and deep alleys, have a slightly above-average park factor at 101. Meanwhile, Reading, with a park factor of 107 can expect about a 7% increase in scoring as compared to a perfectly average park but First Energy Park has a home run factory of 149, indicating that home runs are 49% (!) more prevalent at Reading. Clearwater has a park factor of 113, one of the highest in High-A, while Lakewood has a very low 83, with a 56 (!) home run factor.

So, let’s talk about what this may mean. Games played at Coca Cola park are pretty true to what to expect at any average Major League park but power stats, scoring, and, to some affect, BABIP and HR/9 IP at Reading should be taken with a grain of salt because it is one of the most offense-heavy ballparks in minor league baseball. The same can be said for Clearwater, which in 2014 had  an even higher park factor and home run factor. In the same token, if a player this year puts up monster offensive numbers for Lakewood in

 Lakewood, you should absolutely take notice.

The reverse becomes very interesting, as well. My colleague Jay Floyd was able to speak to both the Lehigh Valley and Reading and pitching coaches and Reading has a number of exciting young arms that were obtained in recent drafts or acquired in trades. Do not panic if you see a bad outing from any of the five  of Aaron Nola, Jesse Biddle, Zach Eflin, Ben Lively and Tom Windle as they are fighting hard against park factors that make the parks very non-pitcher friendly. In the same token, temper expectation if their stats actually improve if they are promoted to the IronPigs.