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Ellen’s Advanced Baseball Metrics for Relief Pitchers

A primer for all of the advanced baseball metrics for pitching used in Ellen Adair’s “Twelve Days of Free Agent Relief Pitchers.”

Ellen’s Advanced Baseball Metrics for Relief Pitchers

Estimated Reading Time: 2 Minutes

I assume most people reading this site know all of these terms, but if there’s one you don’t know, I don’t want to leave you out! The first day of my “Twelve Days of RPs” also has some introductory material, but I wanted to be able to link to this throughout the series.


This stands for Fielding Independent Pitching, and it looks at the things that are in a pitcher’s control: strikeouts, walks, and home runs, scaled to ERA. This evaluation of a pitcher’s underlying skills can help judge whether or not the ERA reflects the pitcher’s performance. That’s why I say Liam Hendrik’s FIP “supports” his ERA.


More a descriptor of what “should have” happened instead of what did. This takes FIP, but normalizes home runs with the average home-run-to-fly-ball ratio.


Expected ERA. A Baseball Savant/Statcast metric that recalculates ERA based on quality of contact. I prefer using this for my “should have” stat. This doesn’t forecast what we expect moving forward; it’s just a different way of looking at the past.

xBA, xwOBA, xSLG, xwOBAcon

Expected batting average, expected weighted on-base average, and expected slugging percentage, also Baseball Savant metrics, that weigh the quality of batted ball contact. xwOBAcon particularly considers the xwOBA only on contact, factoring out walks, and hit-by-pitches. For pitchers, I’ll be talking about these as the contact against their pitches.


Like wRC+ or OPS+, this scales a pitcher’s performance so that league-average is 100, and anything above that is better. (ERA- also exists so that a lower number is better, as with a lower ERA, but I use ERA+ because I like having a similarity between these two stats for pitchers and hitters. So: higher number = good.)


Swinging Strike Rate. For pitchers, the percentage of swings-and-misses out of all pitches thrown.


Whiff rate. For pitchers, the percentage of swings-and-misses out of all swings.


Hard-hit per nine. The number of balls hit above 95 MPH, scaled to nine innings, as with K/9 and BB/9. Alexander Chase introduced this to me, and to the world, with this excellent article. This becomes key in a couple of the pitchers I examine.

Ellen Adair is an actor, probably best known as Janet Bayne in “Homeland,” Bess McTeer in “The Sinner,” and Bridget Saltire in “The Slap,” but has been in a lot of other TV shows, films, and theater that the truly curious can investigate at As a human being, she is best known for her unhealthy love of baseball. It says so on her business cards. She loves baseball in general, but the Phillies are her life partner. She is the author of "Curtain Speech," from Pen & Anvil Press, and is working on bringing to life a TV series about baseball writers. Connect with her on Twitter at @ellen_adair or Instagram at @ellenadairg.

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