March 16, 2017
One Not-So-Fine Day: Reliever Edition
Earlier this month, I wrote an article that was based on a post that Mitchel Lichtman (aka MGL), sabermetrician and co-author of The Book, wrote on his blog, MGL on Baseball. MGL explored the question—I’m quoting from his title here—“What does it mean when a pitcher has a few really bad starts that mess with his ERA?”
If you already read my initial post, or MGL’s, you can skip to the next paragraph. If not, MGL’s conclusion was, briefly, that if a starting pitcher has two or three really terrible starts—really terrible defined here as eight or more runs allowed in five or fewer innings—that contribute to a season-long runs against average (RA9) of 5.00 or higher, we’re likely to overshoot our projection of the pitcher’s ERA for the subsequent season by 0.2 or 0.3.
In other words, two or three disaster starts have such a strong impact on a pitcher’s seasonal ERA (e.g., Jon Gray, 4.61 ERA overall, 3.86 excluding blowups) that the projection systems like PECOTA take too pessimistic a view of the pitcher for the upcoming season. It’s not like we can ignore bad outings, but maybe we’re letting their large impact on the pitcher’s full season output color our perception.
Commenter matthew_kenerly responded:
I can’t help but wonder if you’ll do this with relief pitchers as well, because the first player I thought of was Santiago Casilla.
Well, Matthew (or matthew_), I hadn’t thought of looking at relievers as well, but that’s a great idea! So here goes.