The Pitchers with the Best xwFIP: April Edition
This past offseason, I introduced the pitching metric xwFIP in a series of three posts. xwFIP is an advanced fielding independent pitching metric that not only takes into account walks, hit batsmen, strikeouts, and homeruns, but also the xwOBA on batted balls. The metric takes into account nearly 100% of plate appearances in its calculation. Moreoever, I have showcased that it has greater predictive power than each of ERA, wOBA, FIP, xFIP, xwOBA, and SIERA in predicting future run prevention performance of a pitcher.
This season, I’ll be posting the xwFIP leaderboard each month so we can see the starters and relievers that are most likely to have continued success, along with the pitchers who have been lucky and unlucky so far.
Photo Credit: Ezra Shaw/Getty Images
The Updated xwFIP
I received a very good comment from reader Light_Saberist on one of my latests posts, in which I compared the predictive powers of xwFIP and FIP.
In order to determine the xHR of a pitcher, xFIP (not to be confused with xwFIP) uses the league average homerun/flyball rate of 10.5% and multiplies that rate by the number of flyballs the pitcher allows. This logic may mitigate some of the luck factors in allowing homeruns and thus strengthen xwFIP as well. I checked that hypothesis, and it was correct!
Photo Credit: Daniel Varnado
Comparing The Predictive Powers of xwFIP and FIP
In my previous post, I introduced an enhanced version of FIP - named xwFIP - which incorporates batted ball data and 100% of plate appearances while remaining completely fielding independent. But how is xwFIP’s ability to predict future pitching success? Let’s have a look.
Photo Credit: The Athletic
Introducing xwFIP: An Expansion of Baseball’s Most Powerful Pitching Statistic
Since Tom Tango introduced Fielding Independent Pitching (FIP) to the baseball community around the year of 2009, the metric has been the gold standard for evaluating pitching performance. Tango has effectively proven that FIP is a better predictor of future pitching success than ERA. FIP’s special sauce is its ability to filter for outcomes that are directly related to pitcher performance—home runs, walks, hit batsmen, and strikeouts. Since it’s difficult for the baseball community to assign credit or blame for groundouts, flyouts, and base hits, all of which are largely dependent on the ability of the pitcher’s fielders, these outcomes are treated equally.
Homeruns, walks, hit batsmen, and strikeouts accounted for only 35.7% of plate appearances (PAs) in 2023. However, if we are able to add batted ball data* to FIP, while keeping the metric completely independent of fielding, we can cover 100% of PAs. In this analysis, I will have a go at doing exactly that.
Photo Credit: Orlando Ramirez/USA TODAY Sports