D-backs Starting Pitchers Too Homer Happy

The Diamondbacks’ starting rotation has the third-worst FIP in the National League. If you’ve been watching this season, you’re probably not surprised by this statistic. The starting rotation is sporting a 4.41 ERA collectively. Surely, it needs to be better than that in order for the team to regain relevance. It seems like drastic changes are needed.

Yet, by looking at the different statistics, we can paint a rosier picture. The starters have a 3.68 xFIP, which is good for fifth in the National League. FIP and xFIP are nearly the same, except that xFIP controls for an average home run rate, while FIP uses the actual home run rate. As you’d expect, the HR/FB percentage was sky high, coming in at 12.4%, which was better than only the Rockies. The bullpen, on the other hand, has a 9.8 HR/FB percentage, which is decidedly average. I looked at the bullpen’s home run rate to see if the stadium was part of the problem. Chase Field is known as a hitter’s park, but I wasn’t sure about the homer rate.

Luckily ESPN has a nifty statistic that tracks the effects of different ballparks. Chase Field is the fifth-most conducive to home runs, conceding 1.19 home runs for every 1 home run that would occur at an average ballpark. That explains much of the problem; they’re expected to give up 19% more home runs at Chase Field. We can’t conclude that the D-backs starters are going to give up 19% more homers – they only play half of their games at home. I wanted to test this quickly. From 2000 to 2010, the median HR/FB percentage was 10.7. The D-backs’ rate across that time frame was 11.9%. Now, there are things that can skew these statistic, like having Clayton Kershaw pitch more home games than away games, but it confirms my suspicions. Chase Field gives up more home runs than the typical park.

The ballpark has been part of the problem, but bad pitching has contributed in 2014. Wade Miley, the D-backs’ leader in innings pitched, is the poster boy for bad HR/FB rates. It’s at an astonishing 14.3% — about 50% higher than average. Eighteen of the 23 home runs he’s given up have been at home, and batters have slugged .160 points higher against Miley at Chase Field. This hasn’t been the case in the past, and it’s not like the ballpark changed in 2014. Part of the explanation may lie in the ballparks Miley has pitched at this year. I’m going to list the cities along with their ballpark’s home run rate ranking in parentheses. Miley has pitched at Colorado (1), Los Angeles Dodgers (6), Chicago Cubs (17), San Diego twice (22), Chicago White Sox (14), St. Louis (20), Houston (8), Pittsburgh (29), Atlanta (10), San Francisco twice (30), Philadelphia (7), Cincinnati (4), Miami (24), and Washington (28). Throughout the season, Miley pitched in road ballparks that amounted to being a little less homer friendly than average. Okay, so ballpark factors are contributing to Miley’s problems, but they don’t tell the whole story. His struggles are beyond the scope of this post.

Josh Collmenter has a good HR/FB rate of 8.9, but Chase Anderson has been bit by the home run bug too, with a 13.6 HR/FB percentage. Trevor Cahill and Mike Bolsinger have given up more than their fair share of home runs as well. The ballpark isn’t helping the cause, but quite frankly the starting pitchers must be better. If they want to succeed in 2015, they need to figure out how to give up less home runs.