Zimmerman: Comparing pitcher first-half and second-half performances

From SABR member Jeff Zimmerman at The Hardball Times on February 19, 2016:

Baseball is full of narratives fans and writers can just make up, and no one can easily fact-check them. I don’t think the people making up the narratives do it intentionally, but they see a few facts fitting their preconceived notions and use confirmation bias to solidify their point every time they see another example.

One such example is about certain pitchers breaking down as the season goes on. The discussion’s main focus usually centers on rookies and other young pitchers being unable to carry a full-season workload. Another example is the theory I heard recently is that smaller pitchers wear down more quickly. When looking at pitchers’ first- and second-half splits, sometimes a pitcher performs worse, but most of the time there is no change.

The pitcher I kept hearing about wearing down last year was Taylor Jungmann. In the first half, he was lights out with a 2.15 ERA (3.33 FIP), but it ballooned to a 4.79 ERA (4.29 FIP) in the second half. Some of the increase could be attributed to simple regression or even survivor bias. (Since he pitched above his ability in the first half, he was therefore allowed to pitch consistently in the second half.)

Read the full article here: http://www.hardballtimes.com/comparing-pitcher-first-half-and-second-half-performances/

Originally published: February 19, 2016. Last Updated: February 19, 2016.