The Chicago Cubs’ acquisition of Aaron Bummer would have been great three years ago, but unfortunately, the veteran left-handed reliever probably isn’t good anymore. Maybe the Cubs are hoping that all Bummer needs is more time to recover from his shoulder injury that knocked him out of action for the final five weeks of the 2025 season because he was awful to begin the 2026 season with the Atlanta Braves.
Bob Nightengale was the first to report that Bummer agreed to a minor league deal with the Cubs on Wednesday. The 32-year-old was recently released by the Braves on May 19, after he recorded a 7.63 ERA in 15.1 innings.
Bummer used to be one of the most underrated relievers in MLB when he was pitching for the Chicago White Sox. From 2019-22, Bummer made 161 appearances with the White Sox. During those four seasons, the left-handed reliever recorded a 2.59 ERA, with a 27.2 K% and 71.1% ground ball rate. That was elite stuff from Bummer, who signed a five-year, $16 million contract that included options for 2025 and 2026.
Following the 2023 season, the White Sox continued to tear down their roster, and Bummer was traded to the Braves in exchange for five players: Michael Soroka, Jared Shuster, Nicky Lopez, Braden Shewmake, and Riley Gowens.
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Bummer rebounded after a poor year and recorded a 3.58 ERA in 55.1 innings with the Braves in 2024. Following the season, he and the Braves restructured his contract, which guaranteed him $2.5 million in 2025 and $9.5 million in 2026. The left-hander had another decent year in 2025, but there were signs of decline: a 3.81 ERA and a strikeout rate of only 21.7%.
And that kind of brings us to today. I, and many Cubs fans, would have been ecstatic about getting an elite lefty reliever, but that’s just not Aaron Bummer anymore.
Aaron Bummer’s Decline
2024: 3.58 ERA, 2.23 FIP, 2.52 xFIP, 28.3 K%, 7.4 BB%, 59.7 GB%, 93.7mph average fastball velocity
2025: 3.81 ERA, 3.52 FIP, 3.68 xFIP, 21.7 K%, 7.2 BB%, 53.9 GB%, 91.6mph average fastball velocity
2026: 7.63 ERA, 8.62 FIP, 5.55 xFIP, 16.9 K%, 13.0 BB%, 46.2 GB%, 90.3mph average fastball velocity
So, you have a guy who was throwing 94-95mph early in his career, who was an elite ground ball pitcher, who has now lost velocity for the past three years, and during that time Bummer’s strikeout rate has declined, and so has the ground ball rate.
Again, maybe this year’s struggles have to do with Bummer’s shoulder injury last August, but given that the Cubs need as many arms as possible, you do have to keep putting lines in the water and hope something works.
I’m not holding my breath on this one, but we’ll see how Bummer looks down in Triple-A in the next few weeks.
