<img alt="St. Louis Cardinals v Atlanta Braves - Game Two" src="https://cdn.vox-cdn.com/thumbor/6J8xk8AhRFsl-TKU0jevFL_JS4E=/0x0:8295x5530/1310x873/cdn.vox-cdn.com/uploads/chorus_image/image/73772700/2162235672.0.jpg">
Not even astonishingly-bad BABIP luck could keep 2024 from turning into a bummer for this guy. Good left-handed relievers should be cherished, and Aaron Bummer fits the bill in that regard. The Atlanta Braves picked him up in a trade in November 2023 and despite the fact that it took five players leaving in order for the Braves to bring him in, it ended up being a pretty lopsided trade in favor of the Braves. Bummer was expected to deliver solid production out of the bullpen and while he had to deal with tough luck and the relief corps variant of a lack of respect, he delivered the goods and then some.
How acquired
The Braves sent Michael Soroka, Jared Shuster, Nicky Lopez, Braden Shewmake and Riley Gowens to the White Sox in exchange for Aaron Bummer. The Braves already figured to have a good bullpen heading into the 2024 season and they were able to turn five players that they didn’t regard all that highly and/or have a way of fitting onto the 2024roster into a southpaw reliever who could hopefully provide a real boost to their relief corps.
What were the expectations?
Again, it was expected that Bummer would come in and be a reliable lefty option coming out of the pen in whatever medium- or high-leverage situations A.J Minter didn’t get. Bummer had a pair of fWAR seasons where he was worth at least 1.0 in fWAR (2019 and 2021) and he was coming off of a season where he produced 0.8 fWAR over 58 innings (despite having an ERA of 6.79 in 2023 — he had a normal looking FIP of 3.58, so there’s that), so it was clear that the Braves were hoping that Bummer could continue to be a weapon coming out of their bullpen.
Actually, it’s probably important not to undersell his past success. Coming into 2024, Bummer’s 81 FIP- in 2023 was his highest since his debut season (career 76 FIP-). Same goes for his xFIP- (82 in 2023, 76 career). Basically, he was a dominant reliever whose value was only really modulated by a downtick in 2023, a few injuries here and there, and the fact that he was used in a matchups capacity and therefore didn’t rack up gaudy innings totals. Put those together, and a repeat of his 2023 around 0.8 fWAR was a reasonable expectation, even if that’s a risky thing to project for any reliever given how volatile they are.
2024 results
As it turned out, Bummer was indeed able to deliver a productive season on the mound; he rebounded from his 2023 and then some.
Bummer finished with a much lower ERA of 3.58 and an ERA- of 86 (though those numbers could’ve been much lower had he gotten even a normal amount of luck — more on that, later). He finished the year with an fWAR of 1.1, which qualifies as the third-highest mark of his career. While Bummer’s strikeout rate went down to 28.3 percent (which is an average number for his career and not a precipitous drop or anything like that), he did improve his walk rate by cutting it to just 7.4 percent. That was the lowest walk rate he’s finished with since he walked a very nice 6.9 percent of batters that he faced over 31 2⁄3 innings pitched in 2018.
All-in-all, he finished with an 86/57/63 line (ERA-/FIP-/xFIP-), with the FIP- being the third-best of his career and the xFIP- being the second-best.
Aaron Bummer has also built a career off of inducing a ton of ground balls and 2024 was more of the same for Bummer. He finished the year in the 98th percentile when it comes to ground ball percentage, as 59.7 percent of the batted balls he faced ended up being grounders. Conversely, his fly ball rate went down to 18.8 percent for 2024, and he had a HR/FB rate of 7.1 percent, which was the lowest he put up in a full season since 2018.
Essentially, Aaron Bummer pitched like a high-leverage reliever, but instead he wasn’t really given too many opportunities in high-leverage despite the performance. His leverage numbers were much, much lower in 2024 with the Braves than they were at nearly any point in his tenure with the White Sox outside of his earliest appearances at the big league level (more on this later as well). Still, when he was called upon things usually went well for Bummer and as such, he delivered what was promised as far as his reputation as a reliever goes.
What went right?
Aaron Bummer is very good at getting to two-strike counts and he continued to make it happen in 2024. He was also very solid when it came to taking care of business once he did get to two strikes in the count. He had an ERA of 0.25 and a FIP of 0.41 on two-strike counts in 2024. For comparison’s sake, Raisel Iglesias and Joe Jiménez were the only two relievers who finished ahead of Bummer in fWAR in 2024 and Iglesias’s ERA/FIP in that situation was. 0.46/0.81 and Jiménez went 0.00/0.88 in that regard. Aaron Bummer was essentially going stride-for-stride with the high-leverage guys in Atlanta’s bullpen.
It sure would’ve been nice if he had gotten more of a chance to show off what he had in high-leverage situations but I’m certainly not about to complain about what he did whenever he was out there. All you want out of any given reliever is to be reliable and Bummer was definitely reliable whenever he was out there.
Because of Braves’ ostensible allergy to using Bummer in higher leverage, as well as his inheritance of Luke Jackson’s ghosts or whatever, looking at his season WPA-wise just gives the impression of a sordid mess. His highest-leverage outing, for example, came in the 11th inning against the Phillies on September 1. Bummer got a shallow flyout to prevent the runner from moving, issued a walk without the platoon advantage, and then got a forceout. That set up the Braves to go to the 12th if Grant Holmes could get Nick Castellanos out, but he couldn’t. And yeah, that was not only Bummer’s highest-WPA game of the season, but he didn’t even have another that was particularly close. For a guy with his level of performance, that’s absurd.
What went wrong?
Bummer is a bit of a unicorn in that he routinely somehow manages to end up with his FIP numbers outperforming his ERA numbers. (Coming into the season, he had a career 89 ERA-, a 76 FIP-, and a 76 xFIP-.) Sure enough, that happened again in 2024 but in this case it was a bit ridiculous. Bummer finished with a career-low full season FIP of 2.23 and a FIP- of 57, which was nearly 30 points lower than his ERA-. His xFIP- was 63, so it definitely wasn’t a fluke. Only 15 pitchers in 2024 had 50-plus innings and a bigger ERA-FIP gap than Bummer;
Why am I putting this in the “What went wrong?” column? Because it’s really fun to imagine what it would’ve been like had he actually gotten things to go his way on a regular basis when the ball was put in play. Bummer ended up with a BABIP of .386, which is pretty wild. In fact, that BABIP of .386 was the worst among all qualified relievers in Major League Baseball in 2024. Yes, you read that right: He was rock bottom. Gregory Soto was the “runner-up” with a BABIP of .371, which means Bummer was essentially in a league of his own when it came to BABIP going against him.
If you look at his Batting Average Against on each of his pitches in 2024 and compare it to the Expected Batting Average Against on those same pitches, it’s a bit wild to see the difference.
<img alt=" " data-mask-text="false" src="https://cdn.vox-cdn.com/thumbor/dGC2zwxukWwS7xefJVFvExAVtYI=/400x0/filters:no_upscale()/cdn.vox-cdn.com/uploads/chorus_asset/file/25778017/bummer_xba.png">
Baseball Savant
Since BABIP is a bit of a crude measure, we can also tell you that among any reliever with 100 or more batters faced, Bummer had the sixth-widest gap between his xwOBA and wOBA, and five of those relievers faced 160 or fewer batters, compared to Bummer’s 244.
Bummer surrendered 61 hits on the year, which was the most of any pitcher in Atlanta’s bullpen, with Jesse Chavez coming up just one hit shy of tying Bummer in that regard. Despite giving up the most hits of anybody in the bullpen, he had more strikeouts and fewer innings pitched (69 SO, 55.1 IP) than Raisel Iglesias did (68 SO, 69.1 IP).
Let’s be clear, too: this wasn’t some case of the Braves having a reliever whose skillset was problematic relative to the rest of their roster. The 2024 Braves finished 14th in infield OAA; they finished 16th in infield OAA against lefties. Baseball Savant lets you drill down by OAA by pitcher on the mound, too, and here we see that the Braves’ infield had a whopping -4 OAA while Bummer was pitching, and the team had -6 OAA while he pitched overall. It’s not like being a lefty who elicited soft contact was somehow confusing for the defenders, either; the Braves had +9 OAA as a unit while Max Fried was pitching, which was one of the top pitcher-team OAA marks in baseball. This was basically just the baseball gods and/or relief pitcher poltergeists deciding to victimize Bummer during his first season in Atlanta.
The whole usage thing deserves some discussion, too. Bummer’s seasonal gmLI, which is the average leverage when entering a game, was 0.75. That made him the second-least-leverage-laden (say that five times fast) reliever on the team other than Jesse Chavez, though Luke Jackson also ended up even lower after being acquired.
The die seemed to be cast early on — in his second appearance of the season, Bummer entered with a one-run lead and left with a two-run deficit thanks to: hard single, grounder through the infield, soft bloop over the infield, grounder through the infield. (It was his worst appearance of the season, WPA-wise.)
It took him a month to get back to steady higher-leverage work, but on June 9, he came in with the Braves already trailing and the bases loaded and allowed a first-pitch soft liner double to C.J. Abrams, and was basically banished to meaningless appearances thereafter. If you wanted to be charitable to the Braves and their decision-making, you could say that the reason they did this is because, deserved or not, the game ended up being blown when Bummer was pitching. He finished with six shutdowns and nine meltdowns; amid the 14 appearances that began with him entering the game in above-average leverage to any extent, he collected six shutdowns and had five meltdowns, which isn’t really a ratio you want to see. Again, though, those meltdowns had little to do with his actual pitching. His FIPs in them? -2.83, 0.17, 1.17 (the March game against the Phillies), 4.67, 5.42. Yes, the man had a meltdown in an outing with a negative FIP and his worst meltdown in an outing with a sub-1.50 FIP.
Bummer had a very good season but the baseball gods (and maybe Brian Snitker not trusting him to pitch in higher leverage situations) essentially conspired to make sure that it wasn’t a great season.
2025 Outlook
Well, the Braves were presumably happy (or happy-ish, considering their revulsion to using him in important situations) with what Aaron Bummer gave them in 2024 as he ended up signing a contract extension to stick around through the 2026 season. Considering Bummer’s body of work over the course of his career, it’s difficult to envision him having a serious downturn in performance in 2025. Who knows? Maybe his ERA will start looking like his FIP and if that happens then everybody in Braves Country going to be having the opposite of a bummer* whenever they see him pitch. As it is, though, he basically projects heading into his age-31 season the same way he did when the Braves acquired him — a quite-good reliever. Even ZiPS is on board now!
*I was not going this entire article without making a terrible joke. I know y’all were all waiting on it.
<img alt="St. Louis Cardinals v Atlanta Braves - Game Two" src="https://cdn.vox-cdn.com/thumbor/6J8xk8AhRFsl-TKU0jevFL_JS4E=/0x0:8295x5530/1310x873/cdn.vox-cdn.com/uploads/chorus_image/image/73772700/2162235672.0.jpg">
Not even astonishingly-bad BABIP luck could keep 2024 from turning into a bummer for this guy. Good left-handed relievers should be cherished, and Aaron Bummer fits the bill in that regard. The Atlanta Braves picked him up in a trade in November 2023 and despite the fact that it took five players leaving in order for the Braves to bring him in, it ended up being a pretty lopsided trade in favor of the Braves. Bummer was expected to deliver solid production out of the bullpen and while he had to deal with tough luck and the relief corps variant of a lack of respect, he delivered the goods and then some.
How acquired
The Braves sent Michael Soroka, Jared Shuster, Nicky Lopez, Braden Shewmake and Riley Gowens to the White Sox in exchange for Aaron Bummer. The Braves already figured to have a good bullpen heading into the 2024 season and they were able to turn five players that they didn’t regard all that highly and/or have a way of fitting onto the 2024roster into a southpaw reliever who could hopefully provide a real boost to their relief corps.
What were the expectations?
Again, it was expected that Bummer would come in and be a reliable lefty option coming out of the pen in whatever medium- or high-leverage situations A.J Minter didn’t get. Bummer had a pair of fWAR seasons where he was worth at least 1.0 in fWAR (2019 and 2021) and he was coming off of a season where he produced 0.8 fWAR over 58 innings (despite having an ERA of 6.79 in 2023 — he had a normal looking FIP of 3.58, so there’s that), so it was clear that the Braves were hoping that Bummer could continue to be a weapon coming out of their bullpen.
Actually, it’s probably important not to undersell his past success. Coming into 2024, Bummer’s 81 FIP- in 2023 was his highest since his debut season (career 76 FIP-). Same goes for his xFIP- (82 in 2023, 76 career). Basically, he was a dominant reliever whose value was only really modulated by a downtick in 2023, a few injuries here and there, and the fact that he was used in a matchups capacity and therefore didn’t rack up gaudy innings totals. Put those together, and a repeat of his 2023 around 0.8 fWAR was a reasonable expectation, even if that’s a risky thing to project for any reliever given how volatile they are.
2024 results
As it turned out, Bummer was indeed able to deliver a productive season on the mound; he rebounded from his 2023 and then some.
Bummer finished with a much lower ERA of 3.58 and an ERA- of 86 (though those numbers could’ve been much lower had he gotten even a normal amount of luck — more on that, later). He finished the year with an fWAR of 1.1, which qualifies as the third-highest mark of his career. While Bummer’s strikeout rate went down to 28.3 percent (which is an average number for his career and not a precipitous drop or anything like that), he did improve his walk rate by cutting it to just 7.4 percent. That was the lowest walk rate he’s finished with since he walked a very nice 6.9 percent of batters that he faced over 31 2⁄3 innings pitched in 2018.
All-in-all, he finished with an 86/57/63 line (ERA-/FIP-/xFIP-), with the FIP- being the third-best of his career and the xFIP- being the second-best.
Aaron Bummer has also built a career off of inducing a ton of ground balls and 2024 was more of the same for Bummer. He finished the year in the 98th percentile when it comes to ground ball percentage, as 59.7 percent of the batted balls he faced ended up being grounders. Conversely, his fly ball rate went down to 18.8 percent for 2024, and he had a HR/FB rate of 7.1 percent, which was the lowest he put up in a full season since 2018.
Essentially, Aaron Bummer pitched like a high-leverage reliever, but instead he wasn’t really given too many opportunities in high-leverage despite the performance. His leverage numbers were much, much lower in 2024 with the Braves than they were at nearly any point in his tenure with the White Sox outside of his earliest appearances at the big league level (more on this later as well). Still, when he was called upon things usually went well for Bummer and as such, he delivered what was promised as far as his reputation as a reliever goes.
What went right?
Aaron Bummer is very good at getting to two-strike counts and he continued to make it happen in 2024. He was also very solid when it came to taking care of business once he did get to two strikes in the count. He had an ERA of 0.25 and a FIP of 0.41 on two-strike counts in 2024. For comparison’s sake, Raisel Iglesias and Joe Jiménez were the only two relievers who finished ahead of Bummer in fWAR in 2024 and Iglesias’s ERA/FIP in that situation was. 0.46/0.81 and Jiménez went 0.00/0.88 in that regard. Aaron Bummer was essentially going stride-for-stride with the high-leverage guys in Atlanta’s bullpen.
It sure would’ve been nice if he had gotten more of a chance to show off what he had in high-leverage situations but I’m certainly not about to complain about what he did whenever he was out there. All you want out of any given reliever is to be reliable and Bummer was definitely reliable whenever he was out there.
Because of Braves’ ostensible allergy to using Bummer in higher leverage, as well as his inheritance of Luke Jackson’s ghosts or whatever, looking at his season WPA-wise just gives the impression of a sordid mess. His highest-leverage outing, for example, came in the 11th inning against the Phillies on September 1. Bummer got a shallow flyout to prevent the runner from moving, issued a walk without the platoon advantage, and then got a forceout. That set up the Braves to go to the 12th if Grant Holmes could get Nick Castellanos out, but he couldn’t. And yeah, that was not only Bummer’s highest-WPA game of the season, but he didn’t even have another that was particularly close. For a guy with his level of performance, that’s absurd.
What went wrong?
Bummer is a bit of a unicorn in that he routinely somehow manages to end up with his FIP numbers outperforming his ERA numbers. (Coming into the season, he had a career 89 ERA-, a 76 FIP-, and a 76 xFIP-.) Sure enough, that happened again in 2024 but in this case it was a bit ridiculous. Bummer finished with a career-low full season FIP of 2.23 and a FIP- of 57, which was nearly 30 points lower than his ERA-. His xFIP- was 63, so it definitely wasn’t a fluke. Only 15 pitchers in 2024 had 50-plus innings and a bigger ERA-FIP gap than Bummer;
Why am I putting this in the “What went wrong?” column? Because it’s really fun to imagine what it would’ve been like had he actually gotten things to go his way on a regular basis when the ball was put in play. Bummer ended up with a BABIP of .386, which is pretty wild. In fact, that BABIP of .386 was the worst among all qualified relievers in Major League Baseball in 2024. Yes, you read that right: He was rock bottom. Gregory Soto was the “runner-up” with a BABIP of .371, which means Bummer was essentially in a league of his own when it came to BABIP going against him.
If you look at his Batting Average Against on each of his pitches in 2024 and compare it to the Expected Batting Average Against on those same pitches, it’s a bit wild to see the difference.
<img alt=" " data-mask-text="false" src="https://cdn.vox-cdn.com/thumbor/dGC2zwxukWwS7xefJVFvExAVtYI=/400x0/filters:no_upscale()/cdn.vox-cdn.com/uploads/chorus_asset/file/25778017/bummer_xba.png">
Baseball Savant
Since BABIP is a bit of a crude measure, we can also tell you that among any reliever with 100 or more batters faced, Bummer had the sixth-widest gap between his xwOBA and wOBA, and five of those relievers faced 160 or fewer batters, compared to Bummer’s 244.
Bummer surrendered 61 hits on the year, which was the most of any pitcher in Atlanta’s bullpen, with Jesse Chavez coming up just one hit shy of tying Bummer in that regard. Despite giving up the most hits of anybody in the bullpen, he had more strikeouts and fewer innings pitched (69 SO, 55.1 IP) than Raisel Iglesias did (68 SO, 69.1 IP).
Let’s be clear, too: this wasn’t some case of the Braves having a reliever whose skillset was problematic relative to the rest of their roster. The 2024 Braves finished 14th in infield OAA; they finished 16th in infield OAA against lefties. Baseball Savant lets you drill down by OAA by pitcher on the mound, too, and here we see that the Braves’ infield had a whopping -4 OAA while Bummer was pitching, and the team had -6 OAA while he pitched overall. It’s not like being a lefty who elicited soft contact was somehow confusing for the defenders, either; the Braves had +9 OAA as a unit while Max Fried was pitching, which was one of the top pitcher-team OAA marks in baseball. This was basically just the baseball gods and/or relief pitcher poltergeists deciding to victimize Bummer during his first season in Atlanta.
The whole usage thing deserves some discussion, too. Bummer’s seasonal gmLI, which is the average leverage when entering a game, was 0.75. That made him the second-least-leverage-laden (say that five times fast) reliever on the team other than Jesse Chavez, though Luke Jackson also ended up even lower after being acquired.
The die seemed to be cast early on — in his second appearance of the season, Bummer entered with a one-run lead and left with a two-run deficit thanks to: hard single, grounder through the infield, soft bloop over the infield, grounder through the infield. (It was his worst appearance of the season, WPA-wise.)
It took him a month to get back to steady higher-leverage work, but on June 9, he came in with the Braves already trailing and the bases loaded and allowed a first-pitch soft liner double to C.J. Abrams, and was basically banished to meaningless appearances thereafter. If you wanted to be charitable to the Braves and their decision-making, you could say that the reason they did this is because, deserved or not, the game ended up being blown when Bummer was pitching. He finished with six shutdowns and nine meltdowns; amid the 14 appearances that began with him entering the game in above-average leverage to any extent, he collected six shutdowns and had five meltdowns, which isn’t really a ratio you want to see. Again, though, those meltdowns had little to do with his actual pitching. His FIPs in them? -2.83, 0.17, 1.17 (the March game against the Phillies), 4.67, 5.42. Yes, the man had a meltdown in an outing with a negative FIP and his worst meltdown in an outing with a sub-1.50 FIP.
Bummer had a very good season but the baseball gods (and maybe Brian Snitker not trusting him to pitch in higher leverage situations) essentially conspired to make sure that it wasn’t a great season.
2025 Outlook
Well, the Braves were presumably happy (or happy-ish, considering their revulsion to using him in important situations) with what Aaron Bummer gave them in 2024 as he ended up signing a contract extension to stick around through the 2026 season. Considering Bummer’s body of work over the course of his career, it’s difficult to envision him having a serious downturn in performance in 2025. Who knows? Maybe his ERA will start looking like his FIP and if that happens then everybody in Braves Country going to be having the opposite of a bummer* whenever they see him pitch. As it is, though, he basically projects heading into his age-31 season the same way he did when the Braves acquired him — a quite-good reliever. Even ZiPS is on board now!
*I was not going this entire article without making a terrible joke. I know y’all were all waiting on it.
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