An article I wrote with a family member this summer:
Despite a difficult outing earlier this afternoon, Jeff Francis has performed in a way that few other Rockies pitchers have done this season. Overall, he is pitching reasonably well at Coors Field.
As the Rockies’ starting pitching struggled and the losses mounted this summer, we’ve been grappling with several questions. What makes pitchers like Jeff Francis successful at Coors Field, while others are not? Is pitching at Coors Field different? We did a statistical analysis of pitching in Coors Field and found some unexpected answers.
We began by assembling data on all of the pitchers with 200 or more innings pitched in a Rockies uniform. We also looked at pitchers on other teams that have the most experience at Coors Field, a list that includes some of the best ever -- Randy Johnson, Curt Schilling, Trevor Hoffman, and Tim Lincecum. We call these guys the Division Aces.
We defined success and failure, both at and away from Coors Field, in terms of Earned Runs and built a statistical forecasting model. Like others looking at these types of models, we found that Total Bases, Walks, and Strike Outs were statistically significant in predicting Earned Runs. Home runs, ground ball ratios, and the differences between starters and relievers were not significant either within or outside Coors Field.
We found that Coors Field was fundamentally different than other stadiums in one striking fashion: walks were 50% more damaging in terms of statistically being associated with higher Earned Runs in Coors Field compared to elsewhere. As Rockies fans, we have long known that when pitchers lose control and start walking batters at Coors Field, bad things happen -- multiple, clustered hits and walks, usually followed by a visit from the manager. We were surprised, however, at the size of the impact.
Another unexpected result was that the Rockies pitchers we studied have adjusted to the fact that walks are so damaging at Coors Field, and have fewer walks at Coors Field than on the road. In particular, the most effective Rockies pitchers (Aaron Cook, Ubaldo Jimenez, Jeff Francis, and Matt Belisle) have had particularly large differentials in terms of lower walks at Coors. Statistically, the results suggest that a sub-set of Rockies pitchers have very successfully adapted to Coors Field.
As one example, Matt Belisle is the most effective of the current Rockies pitchers in terms of Earned Runs and has far and away the fewest walks per game in Coors Field (averaging around 1.5 per game, as compared to a team average of 3.7 for the pitchers we analyzed). Like several other of the most successful Rockies pitchers, he is far better in Coors Field than outside (Coors ERA of 3.38 versus outside Coors of 4.56).
In contrast, the Division Aces as a whole have not adjusted. Outside of Coors Field, the Division Aces have a combined ERA of 3.65 (as compared to 4.33 for the Rockies pitchers we studied). In Coors Field, however, the Division Aces have an ERA of 5.40 (as compared to 5.30 for the Rockies pitchers studied). The Division Aces also walk far more batters in Coors. Based on these results, Coors Field can be viewed as a neutralizer, allowing potentially mediocre Rockies pitchers to out-perform some of the best in baseball and creating an opportunity for an extraordinary home field advantage.
Like the situation outlined in the book Money Ball by Michael Lewis, this analysis suggests that the market for pitchers in Coors Field – in part, rewarding those who have better control and can walk less batters – may be different as compared to those playing in other stadiums. This could allow the Rockies to take advantage of inefficiencies and acquire pitchers who are more valuable to the Rockies and in Coors Field than they are to other teams. Other factors beyond those we studied, such as type of pitches thrown, might also create disproportional value in Coors Field.
This analysis also generally supports the Rockies experimentation with non-traditional pitching approaches such as the four-man rotation. Coors Field is statistically different than other fields and the Rockies should experiment to be successful.
Although we lack the data to fully evaluate salaries and other critical elements of the decision, the Rockies could potentially exploit these kinds of market inefficiencies as early as this year. As one example, pitchers like Joe Blanton (1.31 BB/9 in 2012) and Kyle Lohse (1.68 BB/9) have expiring contracts in the off-season and with two of the lowest walk rates among starting pitchers, could present more value to the Rockies than they might to other clubs.