If you’ve made it this far onto our platform, we’ve covered some of the more basic pitching metrics and how they attempt to accurately evaluate pitcher performance. In this topic, we will learn about how some of these same metrics are adjusted to account for other factors that influence a pitcher’s ability to prevent runs.
ERA- / FIP- / xFIP- Explained
When it comes to metrics like ERA, FIP, and xFIP, we generally have an idea of what their limitations might be. However, if we want to continue to take these statistics to the next level in their accuracy, it is important to consider factors such as league average trends, run-scoring environments, as well as the ballpark a game is played in.
Consider this: Is it fair to say that two pitchers who had the same ERA are of equal ability if one pitched in an extreme hitter’s park while the other pitched in an extreme pitcher’s park? Further, is a 3.50 ERA better in 2020 than it was in 1998? How about 1975?
This is where stats like ERA-, FIP- and xFIP- come into play.
Because run scoring can fluctuate from year to year, and from park to park, this is a crucial factor that we need to account for when analyzing pitcher performance. All three of these measurements are scaled similarly to OPS+, except lower is better.
ERA- / FIP- / xFIP- is represented by the following and is the same formula regardless of which metric you calculate:
= 100 * ((FIP + (FIP – FIP * (Park Factor / 100)) ) / AL or NL FIP)
In practice, the league average is scaled to 100, and every point from 100 represents one percentage point better or worse than the league average. This means that a pitcher with a 90 ERA- is 10% better than the league average, while a pitcher with a 110 ERA- is 10% below the league average.
So, if you are trying to compare two pitchers on two different teams or the careers of two different pitchers in two different eras, it’s likely more useful to look at their ERA- than their raw ERA.
FIP- and xFIP- work and are measured the same way, just using their respective raw variables. ERA-, FIP- and xFIP- can all be found on FanGraphs player pages for major and minor league pitchers.
Summary
Creating accurate metrics is a lot like making a great recipe. We constantly make iterations and improve each step of the way to adjust and account for things we may not have realized before. ERA-, FIP- and xFIP- are more advanced than their predecessors and continue to dig deeper into the complex science of evaluating a pitcher.
Related Links
ERA- / FIP- / xFIP- | Sabermetrics Library (fangraphs.com)
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