Sidearm Slingers : Aaron Bummer

Credit: Chicago Sun-Times

Aaron Bummer is up now on the bump in Sidearm Slingers to highlight! The left-handed pitcher of the Atlanta Braves has had a well-established 8-year career so far in the Majors. Having pitched all his games out the bullpen, Bummer has earned his reputation as a solid, relied upon lefty reliever that offers teams a different option out the pen with his unique arm slot.

Here is some insights into why Aaron Bummer has been a success:

Biography

Aaron Bummer is a 6 foot, 3 inch / 215 pound left-handed pitcher from Valencia, California. The 31 year old was drafted out of the University of Nebraska - Lincoln by the Chicago White Sox in the 19th round of the 2014 MLB Draft. The lefty would spend a couple of years in the minors before making his MLB debut on July 27, 2017.

Bummer will play his second season for the Atlanta Braves in 2025, after he was traded to Atlanta during the 2024 MLB offseason.

Over 8 years, Bummer has a 18-18 W-L record with a career 3.79 ERA. He has pitched in 327.1 innings, striking out 378 batters, allowing 287 hits and 147 walks.

Credit: Baseball Reference

Looking at his year-over-year stats, you can see how he has been a solid set-up man that goes in right before the closer. While his last year on the White Sox ended with close to 7.00 ERA, his yearly strikeout, runs allowed, and ERA showcased how Bummer has quickly risen to be a key member for whatever team he has played on.

Arm Angle

Aaron Bummer's current arm angle is 7 degrees, relative to if 0 degrees is a flat plane across the pitcher. This is the lowest it's been at in his career.

2020 Arm Angle: 14 degrees

2021 Arm Angle: 15 degrees

2022 Arm Angle: 12 degrees

2023 Arm Angle: 9 degrees

2024 Arm Angle: 7 degrees

In the following video you can see how due to Bummer's sidearm arm angle and his pitching motion, deception is created by how he hides the ball behind his body until pitch release, and the ball "jumps" forth because it is released at a lower slot. The ball goes from behind his back to the release point, skipping the part where hitters normally see and can time a pitcher when their arm goes over-the-top or at a three-fourths slot.

Credit: The Hub for Baseball Highlights

Pitch Arsenal

Bummer had six different pitch types that he threw during the 2024 MLB season. Out of the six, we will only cover four: his main usage of a sweeper and sinker, and then also 4-seam fastballs and cutters. You can see below how the two pitches not covered, changeup (green grouping) and curveball (light blue grouping) are close to pitch movement of other groups. While pitch speeds are different, Bummer's changeup has the same movement as his sinker (orange grouping), but at a slower speed as intended with the pitch. Then, his curveball is grouped close with his sweepers (yellow grouping), just with more vertical drop.

Sweeper (42% Pitch Usage)

His sweeper (combination of slider and curveball) has induced movement (pitch movement effects without gravity in consideration) of -0.7 of vertical break and 15.1 inches of glove side run (into a righty hitter). Notably, out of all of Bummer's strikeouts during the 2024 season, 69% came from the sweeper.

Sinker (40% Pitch Usage)

Bummer's sinker has 0.3 inches of vertical break and 15.2 inches of arm side break (into a lefty hitter). This means that paired with his sweeper, Bummer has two pitches that can move 15 inches right or left, with the harder sinker thrown at 93.1 mph on average running into a lefty/away from a righty, and a sweeper (breaking ball) at 82.3 mph on average that runs into a righty/away from a lefty.

4-Seam Fastball (10% Pitch Usage)

While sweepers and sinkers are his go-to pitches to get batters out, Bummer still uses a four seas fastball 10% of the time with induced movement of10.4 inches of vertical break and 11.1 inches of arm side run. While using a sweeper and sinker 82% of the time, a normal 4-seam fastball offers Bummer a different way to get hitters out when needed. Thrown more to righties, his four seamer has produced solid numbers of a .160 batting average against and a .200 slugging percentage.

Cutter (5% Pitch Usage)

Finally, Bummer's cutter possesses a 42.9% put away % (rate of 2 strike pitches that result in a strikeout) and has induced movement of 3.1 inches of vertical break and 2.5 inches of glove side cut. While not used frequently, the cutter offers a faster speed pitch that can move into righties/away from lefties than a sweeper, and it can be used in different counts and situations than other pitches in his arsenal.

Percentile Rankings and Bummer's Archetype

Looking at Bummer's percentile rankings for the 2024 season, he once again showed his specialty in avoiding barrels connecting with his pitches and producing an extreme amount of ground balls. His 1.3% barrel percentage ranks in the 100th percentile, and is lowest out of all MLB pitchers this past season. His ground ball percentage of 61.3% is ranked in the 98th percentile, and means with his sweeper and sinker (pitches that are generally lower in the zone) he makes the batter hit a ground ball 61.% of the time. This makes him a specialty pitcher and unique in the fact that a coach could use him in late innings situations when a ground ball is especially needed to produce a double play or get out of a jam.

Going along with Bummer's extremely low barrel percentage is his hard-hit percentage of 32.9% (90th percentile) and average exit velocity of 86.6 mph (91st percentile). These all go together to prove that Bummer consistently produces weak contact, ground balls, and picking up strikeouts (K rate of 28.3%, which is in the 84th percentile). These archetypes aid in Bummer limiting runs allowed for his team (expected ERA of 2.90, which is in the 92nd percentile), which is a primary goal for every pitcher.

Conclusion

Possessing a unique side-arm arm slot, Aaron Bummer creates deception that pairs well with his pitch movements. This causes batters to swing and miss over top of the baseball or produce weak contact on the ball. Having Bummer on the mound also helps give the manager and players an idea that ground balls will be coming a majority of the time (61.3% as of last year). Aaron Bummer is a Sidearm Slinger, and his numbers and motion have given him the success he deserves for going on nine seasons in the big leagues.