This unheralded Braves bullpen arm deserves a bigger role in 2025

The Atlanta Braves rewarded Aaron Bummer for using his high strikeout and groundball rates to shutdown the left-handed power bats that populate the NL East, by extending him through 2026.

Baseball Savant tells us that Bummer’s K-rate is in the 84th percentile, his xERA, average exit velocity, and hard-hit ball rate are just above the 90th percentile, and his barrel and GB rates are elite.

Bummer is a sinker-slider pitcher. Stuff+ reveals that the sinker he throws 40% of the time is 12 points below average. Batters slugged the sinker at a .482 rate.

His only above-average pitches are the sweeper he throws 42% of the time, and a curve (that he threw just 22 times and was likely a slider that picked up some odd spin) he throws just 3% of the time. You might be asking, “How does he get all those good rate stats with pitches like that?” Good question.

Bummer generates a ton of groundballs and deserves more high-leverage situations

Batters put the sinker in play with an average EV just under 87 mph and a launch angle of -9°. Batters find it extremely difficult to get enough loft or exit velocity on the sinker to punish its mediocrity. The slider (sweeper, dust mop, whatever) has an EV of 80 mph at 6³; in other words, they hit a lot of ground balls.

Bummer faced 64 left-handed batters and 19 switch hitters this season, allowing only 27 hits in 107 PA, striking out 32 and walking 6. The only lefties to do any damage were:

CJ Abrams – single, double, and four RBI
Freddie Freeman – single, homer, and three RBI (no surprise)
Kyle Tucker – homer
Keibert Ruiz – two singles, and an RBI
Steven Kwan – single, RBI, and
Shohei Ohtani –fielder’s choice, RBI

The other 18 hits didn’t produce a run.

Lefties batted .266/.326/.392 against Bummer. Righties had a better average but their .284/.338/.348 line shows that they didn’t slug as well. However, they drove three times as many runs and scored just short of four times as often when Bummer was on the bump. Almost all of that scoring came when the Braves’ lefty entered the game with runners in scoring position.

Tough luck with frogs on the pond

Entering a game with runners on base is one of the most difficult situations a reliever can face. If those runners are in scoring position, the level of difficulty increases, and most pitchers will post slightly worse numbers. Sample size affects all stats, so I compared Bummer to other lefty relievers who faced at least 50 batters with RISP.

On the season, he held opposing hitters to a .277/.333/.364 line, but the 83 batters who faced Bummer with runners in scoring position posted a .282/.349/.394 line. That .744 OPS was 33rd in baseball.

While Bummer’s K-rate improved to 34%, third-best on that list, his BB-rate slipped to 11% putting him 27th among that group.

Of more concern was the 7.2 run jump that saw him drop to 34th on the list with a 10.70 ERA, and his strand rate dropping from 72% overall to 22nd on the list at 22%.

Note that in the following lists, two of these things can be true at the same time. For example, Bummer left a game with runners on, and the score remained the same.

In the 37 games he entered with the bases empty, he:

Held the lead 25 times,
Allowed runs four times,
Allowed the opposition to extend their lead four times,
Left the game with men on base five times,

He entered games with runners on base 19 times and left with the score unchanged 11 times. He also:

Gave up the lead twice, including one blown save
Allowed the opposition to extend their lead four times
Left mid-inning with men on base four times

The sample size from last season doesn’t warrant the distrust Bummer has with the fans

I know the last bit makes it seem that I’m anti-Bummer, but that’s not the case. Aaron Bummer is perfect for middle-inning relief when he starts an inning and in low to medium-leverage situations.

When I first saw the numbers for the extension the Atlanta Braves gave Bummer, I thought it was an overpay. However, a deeper look showed it was a way for the Braves to retain control, redistribute actual payroll, and save $1M over two years. Bummer essentially gave up a potential $14M and took a guaranteed $13M.

I suspect the Braves pitching gurus will try to find a way to improve his numbers against righties, and I hope they add another high-leverage arm to back up Dylan Lee and allow Bummer to do what he does best.