Jason Hammel and the Oddity of ERA

ERA can be a weird thing at times. I love it, but it doesn’t always reveal the full story. Jason Hammel is the perfect subject. After six years in the Rays minor league system, and three bad stints with the Rays Major League club, he found himself looking up at a logjam of starting pitchers in Tampa Bay. The Rays traded him to the Rockies after the 2008 season in exchange for Aneury Rodriguez.

With the trade to Colorado, Hammel was given a great opportunity to start in the Majors for a full season. Since his arrival in Colorado two seasons ago, Hammel has been nothing but consistent. Take a look at his stats:

Stat	2009	2010
IP	176.2	177.2
FIP	3.71	3.70
xFIP	3.81	3.81
BABIP	.337	.337
K/BB	3.17	3.00
HR/9	0.87	0.91
AVG	.290	.286
LOB%	69.5%	68.6%
WHIP	1.39	1.40
GB%	46.2%	46.7%
fWAR	3.8	3.7
rWAR	1.8	1.7
Batters Faced	770	771
W-L	10-8	10-9

The model of consistency. The odd thing about his numbers, though, is that his ERA has been different each year, and by almost half a run. In 2009, his ERA was 4.33 with an ERA+ of 109. In 2010, his ERA was 4.81 with an ERA+ of 96. With matching FIP and xFIP, and just about every other stat known to man, you would think his ERA would’ve been the same, or close to it, but that’s not the case. His ERA+ tells us that he was above averge in 2009 and below average in 2010. Was he really above league average in 2009 and below league average in 2010? I lean towards no.

So, why was his ERA half a run worse in 2010 than in 2009 while only facing one more batter? I can only find one explanation: Errors.

In 2009, Hammel allowed 94 runs, and in 2010 he allowed 97 runs, keeping with his consistent efforts. In 2009, he allowed 85 earned runs, and in 2010 he allowed 95 earned runs. Over 177 innings, 10 earned runs equals almost exactly half a run.

So, what type of ERA can we expect out of Hammel is 2011? Do we punish him for his fielders’ errors? No, we award him with his peripherals. I’ll lean towards an ERA closer to his 2009 season than his 2010 season, but with ERA being the odd thing it is, Hammel could post the exact seasons he had in 2009 and 2010 and still post a third different ERA. This does not mean that ERA is a bad stat — in fact, I really like it — but it means that we have to look past ERA because, like I said, it rarely tells the entire story.