Zach Duke and Paul Maholm prove that ERA is not always helpful

Or, the next in the “Were we wrong about” series, which is slowly becoming inaccurately named.

Before the 2009 season began, Paul Maholm was coming off of a great season, which seemed to build on the good second half of 2007 that he had. He seemed to be building towards something good. Zach Duke, on the flip side, managed to stay healthy for most of 2008 but for the most part, he resembled the ineffective pitcher he was in 2006 and 2007. Two pitchers moving in different directions.

Enter 2009. Duke’s ERA has dropped nearly a full point from 4.82 to 3.96. His WHIP has dropped from 1.50 to 1.31. He made the All-Star team. Maholm, on the flip side, has seen his ERA jump from 3.71 to 4.46 and his WHIP from 1.28 to 1.44. Suddenly the perception shifted; Maholm has fallen victim to some kind of “Pirate curse” that befalls Pirate starters. Duke, meanwhile, has regained the “magic” he had during his amazing rookie season in 2005. But is that really what happened? Follow after the jump while I try to answer.

I do want to look at the PitchFX for both of these guys and I’ll do that when the season ends, but to some extent the answers are already apparent. Let’s start with Maholm. Look at the last two seasons on his Hardball Times page:

Year *PRC RA FIP FIP-ERA xFIP DER LD% GB% IF/F K/G BB/G HR/G *HR/F
2008 86 3.88 4.20 0.49 4.16 .710 18.6% 53.6% 6.3% 6.3 2.9 0.95 13.9%
2009 60 4.75 3.81 -0.65 4.24 .673 17.8% 52.3% 8.7% 5.6 2.7 0.67 9.0%

I understand that those numbers probably look like a bunch of gibberish to many, if not most, of you, so let’s walk through the important columns. RA is Truns against; just ERA minus the earned component. So we see there’s a big jump for Maholm this year. FIP, though, is a stat calculated to simulate ERA based on strikeouts, walks and home runs allowed, and we see that Maholm’s 2009 number is much better than his 2008 number. His xFIP, which normalizes for home runs to flyballs allowed and is a very good pitching metric, is almost identical from 2008 to 2009; he only jumped slightly this year from 4.16 to 4.24. His batted ball numbers show that he really hasn’t pitched that differently this year. The line drive percentage against him (LD%) isn’t significantly changed, nor is the percentage of groundballs hit against him (GB%). He’s doind a better job keeping flyballs in the infield (IF/F is percentage of flyballs that stay in the infield) and keeping flyballs in the ballpark (HR/F is percentage of flyballs that leave the park; the big drop in HR/F this year is why his FIP and xFIP are so different), which helps compensate for a slightly lower strikeout rate. But really, the big difference is in defensive efficiency (DER), which is the percentage of balls in play that the Pirates have turned into outs behind him. That number has taken a big dip, and his ERA has risen accordingly.

Now let’s look at Duke:

Year *PRC RA FIP FIP-ERA xFIP DER LD% GB% IF/F K/G BB/G HR/G *HR/F
2008 51 5.40 4.46 -0.36 4.81 .685 20.8% 48.2% 8.3% 4.1 2.2 0.89 10.9%
2009 66 4.19 4.32 0.36 4.43 .705 18.9% 47.6% 6.0% 4.6 2.0 1.05 11.7%

Duke has pitched a bit better this year. His strikeouts are up, his walks are down, his line drives are down, and as a result his xFIP has improved by 0.38 runs this year. Still, that dip is almost half the size of the one his ERA has taken and his xFIP is actually worse than Maholm’s. And again, there’s a big difference in DER from year to year.

The changes in DER aren’t unusual. You can look at the career numbers for Duke and Maholm and see that they both vary from year to year, which is exactly why ERA can be unreliable when evaluating pitchers. We think we know what both pitchers have done in 2009, but when you really look at it, they’re not much different than they were in 2009. If they seem to reverse roles again in 2010, no one should be surprised.

Pat Lackey

About Pat Lackey

In 2005, I started a WHYGAVS instead of working on organic chemistry homework. Many years later, I've written about baseball and the Pirates for a number of sites all across the internet, but WHYGAVS is still my home. I still haven't finished that O-Chem homework, though.

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