Image of
Nickname:   N/A Position:   LHP
Home: N/A Team:   WHITE SOX
Height: 6' 3" Bats:   L
Weight: 200 Throws:   L
DOB: 9/21/1993 Agent: N/A
Uniform #: 39  
Birth City: Valencia, CA
Draft: White Sox #19 - 2014 - Out of Univ. of Nebraska
2014 PIO GREAT FALLS   16 22 18 28 6 0 0 0 1 0 0 0.222 2.45
2015 - DL                            
2016 CAR WINSTON-SALEM   4 5 4 1 1 0 0 0 0 0 1   1.80
2016 PIO GREAT FALLS   7 8 7 11 4 0 0 0 0 1 1   3.38
2016 AZL GLENDALE   4 3.2 5 6 2 0 0 0 0 0 0   12.27
2017 IL CHARLOTTE   3 5 5 5 1 0 0 0 0 0 0   1.80
2017 SL BIRMINGHAM   17 33 29 34 16 1 0 0 3 1 3   3.00
2017 CAR WINSTON-SALEM   8 11 10 15 3 0 0 0 2 0 2   4.91
2017 AL WHITE SOX   30 22 13 17 15 0 0 0 0 1 3 0.178 4.50
2018 IL CHARLOTTE   31 30.2 27 30 11 0 0 0 0 2 3   2.64
2018 AL WHITE SOX   37 31.2 40 35 10 0 0 0 0 0 1 0.301 4.26
2019 IL CHARLOTTE   5 7.2 7 6 2 0 0 0 0 0 0   2.35
2019 AL WHITE SOX   58 67.2 43 60 24 0 0 0 1 0 0 0.184 2.13
2020 AL WHITE SOX $370.00 9 9.1 5 14 5 0 0 0 0 1 0 0.152 0.96
2021 AL WHITE SOX   62 56 42 75 29 0 0 0 2 5 5 0.202 3.51
  • In 2011, Bummer graduated from Sunrise Mountain High School in Peoria, Arizona. He accepted a baseball scholarship to the University of Nebraska.

  • In June 2011, the Yankees chose Aaron in the 31st round. But they could not sway him from becoming a Corn Husker. He majored in business administration.

  • In 2014, the White Sox drafted Aaron (see Transactions below).

  • In 2017, the Baseball America Prospect Handbook rated Aaron as the 21st-best prospect in the White Sox organization.


    "Hectic doesn't describe what I have been through during July/August 2017," Bummer said. "I was in Double-A Birmingham; then I was moved up and flew straight into Rochester to join Triple-A Charlotte.  Seven days later, I was in the line to get some food after a game. The pitching coach, Steve McCatty, came up, and said to go to manager Mark Grudzielanek's office.

    "I had no idea what's going on. The first thing that came to my mind was, "Gosh, I'm going back to Birmingham." Mark told me I was going to Chicago. I just kind of sat there with a stupid grin on my face. I didn't know what to say. I tried to make it feel real in my mind, tried to understand what was actually happening. It felt surreal when I walked out of that office.

    "It probably was around 11:00 p.m. that night, and I was on a flight to Chicago the next morning by 8:00. I definitely did not sleep. My heart was pounding all night.

    "When I walked into the White Sox locker room, I was kind of dumbfounded. I didn't know what to do. Adam Engel came over and showed me the ropes. Once I got into my normal routine, things definitely started to settle down. My nerves started to come back to me.

    "That night, we're playing the Cubs, and I get the call to start warming up. My heart starts pounding again. I'm thinking, "Just don't be that guy who throws the ball into the stands."

    "I got loose, took a deep breath, and realized I was going to do this. Pitch in my first big league game.  As soon as I got to the mound, I looked around at the full stadium. It is an awesome environment, Cubs-White Sox. The biggest thing I wanted to do was throw a first-pitch strike to Anthony Rizzo. Just close your eyes, throw it as hard as you can, and hope it goes over the plate. Once that happened, I'm thinking, "This is what I've been trying to do all my life. Let's just have fun."

    'It's a great situation. I am with a lot of young guys in the bullpen who are going through the same thing as I am. Everyone is pulling for each other to do well.  I'm viewing this as an opportunity to state your case to make the Major League roster for next year. There's nothing guaranteed at this level. My goal is to get better every day, and show them what I can do."  (Bummer - mlb.com - 8/7/17)

  • Aaron was getting food prior to a Triple-A Charlotte contest when his life instantly changed.

    "Charlotte pitching coach Steve McCatty came over and grabbed me, took me out of the food line and into our manager's office," said Bummer from his locker at Guaranteed Rate Field prior 6-3 loss against the Cubs. "He told me what was happening, and I just sat there with a dumbfounded smile on my face, not really knowing what to expect, just spitting out gibberish.  It's a moment I'll never forget."

    There wasn't much of a wait between Bummer's arrival and his Major League debut, as Bummer entered in the eighth to face the defending World Series champions. He experienced the highs of baseball by striking out the first batter he faced, Anthony Rizzo, and the disappointments, thanks to Kyle Schwarber's two-out home run.

    "Legs were shaking a little bit. Couldn't really feel the arm," said a smiling Bummer, who got the balls from his first pitch and his first strikeout. "Emotions were going crazy. Heartbeat was racing. But at the end of the day, it was a baseball game, and it was a good experience."

    "He had a smile on his face, and I was kind of joking with Rizzo, like, 'Hey, go easy on this guy, it's his first one,'" catcher Kevan Smith said. "He got strike one on him. He has a really good slider, and Rizzo had a tough time with it."

    After his debut, Aaron was able to talk about and celebrate the moment with his parents, brother, girlfriend and a few family friends in attendance. (Merkin - mlb.com - 7/28/17)  

  • Aaron is married to Amber.

  • May 9, 2020 (Mother's Day): As a young player, Aaron had a Mother’s Day tradition that he is glad to have given up. No, it’s not something like sending flowers to his mother, Kelly, or writing her name on his glove.

    For some reason, Bummer went through a short streak where he seemed to get hurt on the actual day itself.

    “I don’t know if it’s a necessarily good thing,” said Bummer with a laugh. “Growing up, we always played Mother’s Day tournaments. One year, I got hit by a pitch on my wrist and had to go get x-rays. Another year, I broke my elbow and gashed up my leg pretty bad. I still have a pretty cool scar for it. Thankfully over the last five or six years I haven’t been hurt on Mother’s Day, so we are going to kind of hope that tradition keeps coming.”

    Kelly Bummer actually was her son’s first T-Ball coach, and it was her and Aaron’s father, Craig, who were the first line of support for the southpaw. They were the ones driving multiple hours to games throughout Arizona, and it was mom sitting through contests on Mother’s Day itself instead of being at home relaxing.

    Their sturdy home base started Bummer on his way to becoming one of the better setup men in the American League. And after that one brief period, Kelly Bummer doesn’t have to worry about doctor or hospital visits on her special day.

    “It was awesome, and she was awesome, kind of supporting me and my brother throughout everything,” said the married 26-year-old Bummer, whose wife’s name is Amber. “In reality there is no way to repay your parents, your mother or your father, for everything they did for you.

    “They were role models for me, and I hope I can eventually be the same for my children one day. That’s one of the greatest gifts I can give to them is to raise my children in the same light that they raised me.”  –Scott Merkin

  • 2020 Season 

    In an already truncated season, Bummer’s 2020 campaign was shortened by injury.

    Despite that, the lefy reliever was still able to strikeout batters at a historic rate. Bummer averaged a whopping 13.5 strikeouts per nine innings in his nine appearances for the 2020 Sox.

    That number was the highest ever by a Sox lefty with at least seven appearances and second only to Tommy Kahnle, who averaged a robust 15 strikeouts per nine innings in 37 outings for the 2017 Sox.  (Oct 17, 2020 - SOXNERD)


  • June 2014: The White Sox chose Aaron in the 19th round, out of the Univ. of Nebraska. And Bummer got a $100,000 bonus to sign via scout J.J. Lilly.

  • Feb 22, 2020: Bummer and the White Sox agreed to a five-year, $16 million deal. Bummer will receive $1 million in 2020, $2 million in 2021, $2.5 million in 2022, $3.7 million in 2023, and $5.5 million in 2024.

    The White Sox hold options for $7.2 million in 2025 and $7.5 million in 2026, with $1.25 million buyouts for either season.

  • Bummer is a lefthander. He has a 90-99 mph FASTBALL that grades at least a plus; and a slurvy breaking ball clocked in the upper 80s, also rated a plus pitch. (Spring 2017)

  • 2017 Season Pitch Usage: 4-seam Fastball: 60% of the time; Sinker 1.2% of the time; Change 3%; and Slider 35.7% of the time.

  • 2018 Season Pitch Usage: 4-seam Fastball 11.8% of the time, his Sinker 54%; Change 3.5%; Slider 20.2%; and Cutter 10.5% of the time. Average velocity: 4-seam 93.7 mph, Sinker 93.7, Change 88.1, Slider 83.7, and Cutter 89.4 mph.

  • 2019 Season Pitch Usage: 4-seam Fastball 5.1% of the time, his Sinker 71%; Change less than 1%; Slider 8.6%; and Cutter 14.9% of the time. Average velocity: 4-seam 95.3 mph, Sinker 95.9, Change 89, Slider 85.5, and Cutter 89 mph.

  • 2020 Season Pitch Usage: 4-seam Fastball less than 1% of the time, his Sinker 83.6%; Slider 7.3%; and Cutter 8.5% of the time. Average velocity: 4-seam 93.4 mph, Sinker 95.9, Slider 83.8, and Cutter 88.9 mph.

  • Aaron has unusually good deception with his delivery.

  • In 2019, hitting against this lefty was quite the bummer. Batters posted a .235 wOBA in 262 plate appearances against Bummer, which is actually a few points worse than the offensive output of Austin Hedges in his 347 trips to the plate (.242 wOBA). Bummer was clearly doing something right, and much of his success can be attributed to his 72.1% groundball rate, which ranked only second to Zack Britton’s (77.2%) among qualified relievers. In fact, Bummer’s 2019 groundball rate was the ninth-highest of all 1,417 qualified reliever seasons during the 2010s. (Devan Fink - Feb. 6, 2020)

  • In 2017, Aaron was sitting in a restaurant when his career path as a pitcher took a major step forward. He actually isn't positive of the exact restaurant. But he does remember a dinner conversation with Ryan Riga, his teammate with Class A Winston-Salem at the time, concerning a change of approach with his sinker.

    “We were sitting at an Applebee’s or something after a game and watching Zack Britton pitch, and we were like, ‘That thing is disgusting. How are we going to figure that out?’” Bummer said. “We went on YouTube that night, found out how he was gripping it, and spent the entire next day during BP playing catch for 45 minutes trying to figure out what he was doing.

    “That was kind of, we found something, we found something that worked. We found something that sinks. So, we were like, ‘Here we go.’ It’s something different. It’s not the way most people throw. But it works for me.”

    Bummer previously was throwing a different variation of the two-seamer but took his fingers off all the seams when throwing the new and improved sinker. At first usage, Bummer laughed when describing how he got his teeth kicked in. But that sinker now has become a dominant pitch. Bummer jumped four levels in 2017, ultimately finishing with a 4.50 ERA over 30 games with the White Sox.

    In 2018, he posted a 4.26 ERA over 37 games. But in 2019, he became a late-inning piece, as shown by his 2.13 ERA, 27 holds, and just 43 hits allowed in 58 games and 67.2 innings.

    According to Statcast, Bummer ranked second behind none other than Britton with a 71.4 percent ground ball rate in 2019. He also allowed the fifth-lowest expected slugging and was tied for the fourth most vertical movement on sinkers at 6.5 inches more than average, based on other sinkers thrown at similar velocities. It’s a pitch at the core of his new five-year, $16 million contract.

    “Really, ever since I found it in Winston-Salem in 2017, I haven’t touched it. I haven’t tried to manipulate it,” said Bummer of his sinker. “That’s one of the reasons why I’ve grown to have success with it. I’m trying to throw the ball down in the zone to the best of my ability. At the end of the day, I’m going to live and die with that.”

    For some reason, Bummer doesn’t need a seam to be able to feel the baseball on his sinker thrown at an average velocity of 95.8 mph in 2019, per Fangraphs. Jace Fry, another talented lefthander in the White Sox bullpen, has talked with Bummer about his sinker, according to Bummer, but can’t command it without the seams.

    “Thankfully it worked out pretty well,” said Bummer, who also features a cutter and occasionally mixes in a four-seamer, changeup and slider. “Hopefully it’s there the rest of my career.”

    Manager Rick Renteria recounted a story Saturday of having a talk with Bummer, who was expressing how excited and impressed he was watching Michael Kopech, Dylan Cease and Dane Dunning throwing sides. Renteria quickly let Bummer know he wouldn’t want to sit in the box with Bummer pitching either.

    “He can get a lot of ground balls for us in big situations. We are not afraid to use him in any situation,” Renteria said. “This is 95, 96, 97. I mean, with some sinking action. It’s pretty special.”

    This journey unofficially began at Applebee’s, by watching Britton in action. Other young hurlers looking for an edge might be studying Bummer’s sinker in the not too distant future, causing Bummer to smile and shake his head in almost disbelief.

    “There’s so much information out there,” Bummer said. “You can go watch 'Pitching Ninja' videos and they will show you exactly how certain people are throwing it. You have every opportunity to go out there and figure something out or change a grip or mirror somebody. The information you are able to get now, it’s a blessing. It really is, to go out there and figure things out that way. It’s just being able to find command with it and being comfortable with changing the grip and changing something. You just kind of look at yourself and say what you want, are you willing to take the lumps and bruises that changing something might take.”   (Scott Merkin - Mar. 8, 2020)

  • 2019 season: Bummer put together one of the best seasons among AL relievers. The 26-year-old posted a 2.13 ERA over 58 games with 60 strikeouts in 67.2 innings, a 0.99 WHIP and 27 holds.

    He ranked among the AL relief leaders in inherited-runners-scored percentage (17th, 19.4), first-batter efficiency (fourth, .115), holds (sixth, 27), ERA (seventh), and opponent average (ninth, .184).

  • August 2020: During a home game against Cleveland on Aug. 7, Bummer’s season almost came to an end. He left after a two-out throwing error on Cesar Hernandez’s grounder back to the mound and an ensuing pitch to José Ramírez that followed a visit from the head athletic trainer in the seventh frame, but he actually felt something fairly severe in his left biceps a little earlier in the game as part of his second relief inning.

    “Oh, it felt like a knife was going through my biceps,” said Bummer. “It was a feeling that I never had before. I’ve had Tommy John. I’ve had a bunch of things wrong with my elbow. I’ve gone through all those things, and this didn’t feel like any of that.

    “There were two outs, and I kept kind of looking up at the radar gun seeing, ‘OK, this kind of hurts but I must be OK, if my velo is holding.’ I kind of kept going, and I don’t think I made it anything worse than what it was, but kind of threw the last pitch to José Ramírez and it was definitely the smartest decision to take myself out of the game and see where I’m at.”

    Bummer’s injury was more nerve-related than a strain, meaning it took a little longer to find the extent of the problem and an appropriate rehab course. He returned on Sept. 24 and made two scoreless regular-season appearances, and then he added two more scoreless efforts in the American League Wild Card Series vs. Oakland. Bummer's work to get fully healthy has continued in the offseason, with a few more boxes to check off, he said.

    “It was more of a typical maintenance program of re-strengthening my biceps and keeping on the things we were doing just to make sure, going into Spring Training, I was going to be in a great spot,” Bummer said. “There wasn’t a prescribed rehab, and it wasn’t about knocking this stuff out. It was more, let’s keep the progress going in the right direction.

  • 2020 Season: Bummer had some injury trouble in 2020 but when he was out there he was filthy. In 9.1 innings (over nine appearances), he had an ERA of 0.96 and a WHIP of 1.071 with 14 strikeouts.

  • 2021: Referring to Aaron as the White Sox setup man accurately depicts his important bullpen role for the upcoming season. This depiction also sells short Bummer’s overall value in getting the baseball from White Sox starters to new closer Liam Hendriks. Look at the 27-year-old as more of a high-leverage force for a team with World Series championship goals.

    “Regardless of whether it’s the sixth, seventh or eighth inning, I want to go out there and get as many outs as I can,” Bummer told MLB.com. “And I love the feeling of the leverage stuff and knowing that the game is in the balance. The game can shift one way or the other: whether it’s getting a ground ball with runners on base to get out of a jam, [or] getting a double play to end the sixth and then being able to go out there and throw the seventh.

    “I kind of thrive on that situation. I trust the rest of the bullpen and I hope the coaching staff trusts the rest of the bullpen as well to go out there and get all those outs. I’m not going to sit here and say I want the eighth inning, or I want this. I’m going out there to pitch and help in any way possible.” 

  • “As we stand here today, I’m 100 percent full-go, ready for Spring Training. I’m in a good place.”

    That good place for Bummer, whose devastating sinker has helped him produce the second-highest groundball rate among relievers over the past two seasons, should mean good things for the White Sox. Those good things could come in the eighth or the sixth or even across two innings, if needed.

    With one of the best overall bullpens in the game, the White Sox have the luxury of using one of their best relief weapons in the toughest situations.

    “If I make my pitches, I’m going to win,” Bummer said. “That’s kind of the way I feel. You have to have the confidence going out there on the mound,” Bummer said. “It doesn’t matter, righthanded or lefthanded. If I make my pitches, I’m better than the other person.

    “That’s the mindset that everyone in our bullpen has. Everyone trusts their stuff. Everyone trusts their ability, and when we are doing that, at the end of the day, we will have a lot of success.” (S Merkin - MLB.com - Jan 19, 2021)

  • Bummer’s has been in the Majors since 2017. In five seasons, he has posted groundball rates of 54.4%, 61.2%, 72.1%, 68.4%, and 73.7%. Over that time frame, he ranks fourth in groundball rate among all pitchers who have tossed at least 50 innings. The leading culprit behind his prolific groundball rates is his sinker. (Carmen Ciardiello - FANGRAPHS - July 19, 2021)

  • As of the start of the 2022, Aaron had a career record of:  7-9 with a 3.13 ERA, having allowed 12 home runs and 143 hits in 187 innings.

  • 2022 Season: 32 G, 26.2 IP, 25.6% K, 8.5% BB, 2 HR, 2.36 ERA, 3.19 FIP, 0.6 bWAR, 0.3 fWAR

    Looking at the above stat line, one might assume that Bummer was a stalwart in the bullpen when he was healthy, but that couldn’t be further from the case. His Win Probability Added (WPA) was -0.50 for the season, and to make matters worse, he did most of his best work after the Sox had been de facto eliminated. Bummer struggled badly with control in April, and while he only walked two batters the rest of the season, struggles with stranding inherited runners persisted. Nine meltdowns against five shutdowns isn’t going to cut it, regardless of your peripherals.  (PATRICK NOLAN
    OCTOBER 19, 2022)

Career Injury Report
  • 2015: Bummer missed the entire season.

  • June 16-July 19, 2016: Aaron was on the D.L.

  • Aug 8-Sept 24, 2020: Bummer was on the IL with a left biceps strain.

    Bummer, 26, departed in his second inning of work, after throwing a 95.2 mph sinker to José Ramírez and then calling for the trainer and Rick Renteria. The White Sox manager said the severity of the injury was not yet known.

    “Hopefully, it’s not anything of significance,” Renteria said.

    Sept 12, 2020: Bummer has been dealing more with a nerve issue near the muscle of late.

    Sept 19, 2020: The White Sox remain hopeful that they will be able to add one of their strongest bullpen weapons to their postseason roster.

    Bummer threw a 20-pitch simulated game at Great American Ball Park in Cincinnati, prior to the Sox game with the Reds. Bummer has been sidelined since early August with a left biceps strain and a nerve issue near the muscle that developed after the initial diagnosis.

    "He looked good—really, really good," manager Rick Renteria said of the simulated game. "He says he feels good, so we're very positive about how he's progressing."

  • June 28-July 15, 2021: Bummer was on the IL with a right hammy strain.

  • May 7-22, 2022: Bummer was placed on the injured list with a right knee strain.

  • June 9-Sept 5, 2022: Bummer was on the IL with left lat strain.