ERA- is the stat of the future because it has context built in. The issue with classic ‘earned run average’ is that a 4.00 ERA is vastly different in 1995 compared to 2015. The reason is because the run scoring environments are different. In the 90’s everyone was on steroids hitting 500 foot home runs, there for a 4.00 ERA was below league average making Pitcher A a solid starter. Now fast forward to 2015 to a league dominated by hard throwing young pitching, now that 4.00 ERA is above league average (pitcher B). If your using classic ERA , Pitcher A and B have the same ERA and should be valued to same. However we know that they are not because of what we just discussed above, Now lets get into ERA-.
First lets get used to what ERA- looks like, it’s scaled so that 100 is always average.
So, let’s say the average ERA is 3.80 in 2015, and Morrow has a 3.00 ERA. His ERA- would be something like 88, or 12 percent better than league average.
This stat lets you compare pitchers to the league average, so you know how good they really are. It also lets you compare players from different era’s that played in different run scoring environments.
Learn everything you need to know about ‘ERA-‘ in this week’s Taylor Metrics podcast.