Aaron Bummer

Bummer had one of his worst statistical seasons over his seven-year career in 2023. His 6.79 ERA was highest in the league among qualified relievers, while his 1.53 WHIP was 12th-worst. This is mostly due to an elevated 13.5% walk rate (his worst since his rookie season), high BABIP (.340) and poor 55.4% left-on-base percentage. However, Bummer's inflated ERA was far worse than his 3.58 xERA, suggesting he should rebound in that category. The veteran is still one of the best in the league at inducing ground balls, but Bummer threw fewer sinkers (45% pitch usage) last season in favor of more sweepers (38%). This adjustment yielded a career-high 78 strikeouts, which speaks to the upside the southpaw possesses. Bummer was recently traded to Atlanta, where he could emerge as one of the team's top setup options in 2024.

Bummer required two IL stints in 2022, first a minimum stay early in the season for a sore knee, then a more lengthy 3-month absence due to a shoulder/lat injury. This limited the southpaw to only 26.2 innings last season. Injuries appear to be part of the package for the 29-year-old, who has now missed time on the IL during each of the past three years. When healthy, Bummer is adept at inducing ground balls, as his career rate is 67.6%, which is roughly 25% above league average. He walks about four batters per nine innings, though, and the frequent grounders could lead to some BABIP and ratio instability. However, Bummer's role as one of the White Sox primary setup men appears secure, so expect him to provide holds as long as he's healthy.

Bummer proved that his small-sample spike in strikeouts in 2020 wasn't a fluke, as he was once again able to top a 30 K% in 2021 across 56.1 innings. Even better was that he didn't sacrifice his primary identity as a groundball pitcher by turning in his third consecutive season with a groundball rate over 65%. Unsurprisingly, that has helped him limit home runs, and he's been able to limit hitters to 0.6 HR/9 across 187 career innings. In most cases, that combination of skills would lead to a pitcher receiving a look as closer, though Bummer has largely been limited to a setup role throughout his career. That isn't likely to change in 2022, as the White Sox boast a tremendous trio in the back of their bullpen in Liam Hendriks, Craig Kimbrel and Kendall Graveman. While we expect Kimbrel to get dealt at some point later in the offseason, Bummer's value is still likely tied to his strong ratios and plenty of strikeouts.

The closer job for the White Sox briefly opened up after Alex Colome left in free agency, but despite his recent success Bummer was denied a chance to compete for it when the club signed Liam Hendriks. It's tough to get too excited about the 27-year-old lefty's 2020 campaign, as bicep issues limited him to just nine appearances, but Bummer was excellent when available, posting a 0.96 ERA and a 36.8 K%. It's difficult to expect anything close to a repeat of that performance in 2021 given the size of the sample and the fact that he posted a rather modest 22.9 K% during his breakout 2019 campaign. Still, that's now two years where he's looked like a high-leverage option, with an elite 71.7% groundball rate over that stretch keeping him in that tier despite modest numbers elsewhere. He doesn't have a traditional closer's profile, but Bummer should remain in the late-inning mix.

Bummer spent the previous two seasons as an unremarkable middle reliever for the White Sox, but he turned into a high-leverage option in his age-26 season and recorded 27 holds. Overall he had a 2.13 ERA and 0.99 WHIP across 67.2 innings, and he held both righties and lefties to a sub-.200 average. The left-hander interestingly saw his strikeout rate drop (22.9%) and his walk rate rise (9.2%), but he relied much more heavily on his fastball (76.4% usage) and saw an uptick in velocity (95.5 mph) to help induce a 72.1% groundball rate. Barring any free-agent additions, Bummer should enter spring training in the setup role to closer Alex Colome, who went 30-for-33 in save opportunities.

After vaulting up the organizational ladder in 2017, Bummer was rewarded with an Opening Day roster spot. Early on, the southpaw was used almost exclusively in one- or two-batter stints, largely as a specialist. The results were promising, as he posted a 3.26 ERA and a 21:6 K:BB in 19.1 frames before being shuttled back to the minors. He returned to the big leagues for the month of September and was touched up a bit to the tune of eight runs in 12.1 innings. Despite the struggles at the end, 2018 was largely a success for the 25-year-old. His 65:21 K:BB in 61.2 innings between the majors and minors was strong, and he held left-handed hitters to a .245 batting average. Plus, his 2.44 FIP fell well below his 4.26 ERA for the season, suggesting he was the subject of some bad luck. He figures to have a role in the middle innings in 2019.

Last season marked the first complete campaign for Bummer since he underwent Tommy John surgery in 2015. The White Sox started him at High-A, and he pitched at four levels last season while eventually getting the call to Chicago. In the minors, he struck out a batter per inning at each of his three stops, but he struggled to miss bats as a big-league reliever in his debut. Additionally, his walk rate spiked to a career-worst 6.1 BB/9, which kept the White Sox from relying on him in high-leverage spots. There are a few positives, however, including a track record of better control and his ability to get outs on the ground (54.4 percent groundball rate). With a low-90s fastball and slider combo, Bummer should get more opportunities to stick with the White Sox in 2018, but he may wind up bouncing between Charlotte and Chicago if he fails to cut back on the free passes.