ERA+ (and OPS+)
We all know ERA (earned run average), which is the amount of earned runs a pitcher allows per nine innings pitched. Pretty straightforward. Adjusted ERA (ERA+) means the ERA is adjusted to that pitcher’s ballpark (in case the pitcher’s home park is a pitcher’s park such as Petco Park or hitter’s park like Coors Field).
You will see ERA+ numbers as a number around 100. A score above 100 is better than average, below 100 is, consequently, sub-par. Think of it like this: Kyle Freeland of the Colorado Rockies has an ERA of 3.84. Normally, that is considered decent but maybe not All-Star worthy. However, when pitching half of his games at Coors Field in that thin Colorado air, that’s pretty impressive. His ERA+ is 131.
Mariners starting pitcher Ariel Miranda has a very similar ERA at 3.82. However, he pitches in more pitcher-friendly Safeco Field so his ERA is a bit more scrutinized. His ERA+ score is 111. The best pitcher currently according to ERA+ is Max Scherzer with a 212 score. He also happens to boast the best ERA in Major League Baseball at 2.06. That doesn’t always happen. The worst qualified pitcher according to ERA+ is Kevin Gausman of the Orioles with a 71 score.
OPS+ (Adjusted on-base plus slugging) is the exact same idea for hitters. Arizona has one of the better hitter’s parks. One of their best hitters is Jake Lamb. He has an OPS of .929. His OPS+ is 132. Nelson Cruz has a lower OPS at .899 but since he plays in spacious Safeco, his OPS+ is higher at 140.