Opponent OPS

Over the last several years, it's been clear that pitching in Major League Baseball has become more dominant. In fact, it has been over 20 years since the league ERA has been as low as it has been so far this year. This year's MLB ERA is 3.88, the lowest since the 3.75 mark in 1992.

Some of the high points in ERA in that time were 4.71 in 2000, 4.77 in 2001 and 4.53 in 2006. Since 2006 ERA has been trending downward as seen in this chart of MLB ERAs:

ERA is a useful summary statistic, but my favorite stat for pitchers is Opponent OPS. For MLB, overall, Opponent OPS is pretty consistent with ERA, but for an individual pitcher, it is much more indicative of his true pitching performance than ERA. ERA has many biases that Opponent OPS does not have. For example, ERA rewards pitchers who allow most of their home runs with no runners on base or are able to strand runners at the end of innings, even though those events are generally believed to be random and out of the pitcher’s control. Another example is the effect a relief pitcher has on his predecessor's ERA when it comes to stranded runners.

Here are the MLB leaders in Opponent OPS in 2013:

And here are the MLB leaders in ERA this season:

As you can see, the OPS leaders are bit different. Clayton Kershaw and Matt Harvey have been tremendous by any measure. However, that is where the similarities end. Opponent OPS prefers the rookie phenom Jose Fernandez, major-league win-leader Max Scherzer, and Madison Bumgarner while ERA prefers Felix Hernandez, Hiroki Kuroda, and Jeff Locke.