Upon first glance, Joe Blanton appears to be a perfectly average major league pitcher. After all, his career ERA is 4.25  – exactly the same as the league’s ERA during that time. But if we look closer, we see that the newest Philadelphia Philly isn’t actually average; rather, he’s been the beneficiary of pitching over half of his innings in a favorable environment. Namely: McAfee Coliseum.

Joe Blanton has been a very consistent pitcher in his big league career. Every year since 2005, Blanton’s average fastball has been almost exactly 89 MPH. He’s thrown his fastball right around 55% of the time, and he’s thrown his slider, changeup, and curveball approximately 15% of the time each, respectively. His ability to throw his pitches has not changed from year to year.

In 760 career innings, Joe Blanton’s career ERA of 4.25 is exactly the same as the league’s ERA during that time. Blanton has, in other words, been incredibly average. And, considering the fact that he’s been durable as well, his “averageness” is very valuable. But if we look closer, we see that Blanton can thank luck and/or the Oakland Coliseum for some of his success.

In 760 career innings, Blanton has 431 career strikeouts, which equates to a rate of 5.1 batters per nine innings. This is below average, but just high enough to get by. Additionally, he has solid – but not amazing – control, having walked 202 in that span, or 2.4 batters per nine. Blanton has had two seasons of very average luck on balls in play – this year, his BABIP is .302, and last year his BABIP was .299. He has also had two seasons of tremendous luck – both good and bad – on balls in play: in 2006 his BABIP was .335, while in 2005 his BABIP was .248. Of the balls in play against him in his career, 45% have been grounders, 35% have been fly balls, and 20% have been line drives. Those numbers are almost exactly league average.

Blanton has made up for his below-average strikeout rate with an above average “ability” to suppress the long ball.

While approximately 11-12% of fly balls become homers on average, Blanton has given up only 69 homers on 892 career fly balls – good for 7.7%. Much of this likely stems from the fact that he has pitched for the Athletics during his entire career. You can find different sources for park factors, but according to this McAfee Coliseum depresses homers by 11%. When we adjust for the fact that Blanton made approximately half of his starts in the Coliseum, we can see how he was able to beat the league average in homers per fly ball by approximately 4-5%. Sure enough, we see that Blanton’s career HR/9 at home is lower (0.75) than his career HR/9 on the road 0.90).

But McAfee Coliseum is not only helpful for pitchers in suppressing homers, it’s also excellent for helping pitchers allow fewer hits – mainly because the extensive foul territory leads to more foul outs. In fact, Blanton benefited from this: although his walk rate and strikeout rate were virtually identical away from home as they were in Oakland, his hit rate in Oakland was much better than it was on the road. And, as expected, his ERA was also much better in Oakland than on the road.

Blanton’s aggregate ERA was exactly league average (4.25) during this time, but this is mainly because of the fact that he pitched 54% of his innings in a very favorable environment.

Now, however, his home pitching environment has changed. Although he will face generally inferior competition in the National League – and will get to face the pitcher’s spot several times per game – Blanton will likely struggle in Citizens Bank Park. While pitching in Oakland saved 11% of his fly balls from becoming homers, pitching in Philadelphia will increase his homer total by _at least_ 5% (some measures have Citizens Bank Park inflating homers by as much as 16%). Thus, he should give up approximately 16% more homers in his home starts than he would have if he was still pitching in Oakland. Furthermore, Citizens Bank Park has allowed more hits than average, meaning that Blanton will likely struggle not only with increased homers, but also increased hits in general.

Joe Blanton is actually not an incredibly average pitcher, despite his career ERA+ of 100. Rather, he is a somewhat below-average pitcher who has appeared to be average because he has pitched over half of his innings in McAfee Coliseum. Now, although he is switching to the weaker league, Blanton will have to pitch half of his games in a harsh pitching environment. Pitching in Philly will be much more difficult for Blanton, and he will likely be exposed as the below-average pitcher that he is.

Below-average doesn’t mean bad or unhelpful. It just means that if the Phillies are expecting a guy with a 4.25 career ERA (or perhaps expecting even more, due to the league switch), they are going to be disappointed when the guy with the 4.79 career ERA in all games played outside of Oakland shows up and attempts to pitch half of his games in Citizens Bank Park.