Fun With Sabermetrics - Day 2 - ERA+

Sup, boners. Let's get right into it because I'm about to go to Jamba Juice.

ERA+ or Adjusted ERA

Another pretty heavily-weighed stat, this time for pitchers, obvi. It's basically a pitcher's ERA adjusted for ballpark (whether the ballpark is a hitter's park or a pitcher's park) and for the average ERA for the league the pitcher's in. Essentially it takes pitchers who throw in pitcher's parks and pitchers who throw in hitter's parks and plops 'em smack on an even playing field. So let's say a pitcher has an ERA of 4.0 in a hitters park where the league avg. is 4.0. He'd have an ERA+ of 100. For ERA+, 100 is the league average. So you got yourself a pretty average pitcher.

To the formula. To find ERA+ you take the league ERA, multiply that by the home park factor, multiply that by 100, then divide by the pitcher's ERA.

Confusing right? If only there was a player we could use as an example. Oh I know. How 'bout newest Rangers pitcher and recipient of a brand new robot arm, Brandon Webb!

B-Webb had 2 absolutely beast years in his last 2 full seasons. Let's take the most recent, 2008. Webb had an ERA of 3.3 while going 22-7 on the year for the D-Backs. So. According to baseball-reference.com, the '08 ERA avg. for the NL was 4.29. Now Chase Field in AZ is a big time hitter's park. In fact in '08 the only park that batters hit better in was, hi-o, Rangers' Ballpark in Arlington, home of your 2010 American League Champion Texas Rangers. Chase had a park factor of 1.135 in 2008. So 4.29 x 1.135 x 100 is 487, divide that by his ERA of 3.30, and KERSPLAT. You have a beastly ERA+ of 147, meaning he was 47% better than the average NL pitcher in 2008.

Some other notable pitchers with awesome ERA+, that douchebag closer in New York who gets to wear number 42 even though it's retired across the league has the best ERA+ in a career at 202 but who cares because he's gonna die in a fiery inferno tonight. Pedro's mystical 2000 season carried an ERA+ of a ridiculous 291. And Tim Keefe, whose name I only mention because it rhymes with queef, set the alltime record in 1880 with an ERA+ of 294, but that was back before the invention of sabermetrics or television or paper or dinosaurs.

So. There.

-Me.