2023 White Sox in Review: Aaron Bummer

Aaron Bummer is counted on as the anchor of left-handed relief pitching for the Chicago White Sox. Bummer pitched dependably in 2022 despite suffering an injury-shortened season. Given his history, he seemed likely to bounce back in 2023, but the lefty ended up having the worst year of his career. The southpaw's performance can best be described as dismal.

The former 19th-round pick is a streaky arm who's at his best when entering a game with a clean inning. Peripheral statics such as xERA, FIP, and xFIP think highly of Bummer, as he even put together a 0.8 fWAR in 2023. However, the eye test tells a much different story. Bummer pitched to the tune of a 6.79 ERA over 58.1 innings with a 1.53 WHIP, which considerably exceeds his expected ERA of 3.53.

When You're Counted On Goes Wrong

While Bummer did achieve his best K/9 since the 2020 COVID-shortened season, his walk rate rose to nearly a career-high while he posted an almost career-low ground ball rate. Bummer's ability to produce ground balls on weak contact and limit walks is the key to his effectiveness. As a result, only 55.4% of runners were left stranded.

The season went sour on Bummer quickly as he entered May with an ERA over nine. While he put together a nice stretch in June, pitching to a 3.68 ERA in 7.1 innings, he couldn't produce an ERA below six in the final three months. Particularly, the 30-year-old allowed more than half of his 45 runs in high-leverage situations, where he's needed most.