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A deeper look at new Braves reliever Aaron Bummer

If we just look at Bummer’s ERA, adding him is a head scratcher. Spoiler alert, he is much better than his 2023 ERA>

MLB: Minnesota Twins at Chicago White Sox Kamil Krzaczynski-USA TODAY Sports

The Atlanta Braves have added and subtracted numerous players this off-season, which has been quite entertaining for those who enjoy the business side of baseball. One of the players that was brought in that seemed to not get much buzz was Aaron Bummer. It seemed more that the players gave up were talked about more than the excitement of bringing him in.

Of course, this is understandable since the Braves gave up fan favorites such as Mike Soroka, Nicky Lopez, and more in what was seemingly trading contracts that the Braves were considering non-tendering to add a player with high upside (of course, there were multiple variables involved in the trade that makes it more complex).

At first glance, we see that Bummer had an atrocious 6.79 ERA in 58.1 innings. This obviously makes it seem like a head scratcher that the Braves would pull the trigger on bringing him in, but if we dig deeper we can see the appeal.

First, the White Sox had a terrible defense behind Bummer, which certainly does not help his ERA. According to Fangraphs, only eight teams had worse overall defense than the White Sox. On the opposite side of the coin, fourteen teams had better defense than the Braves. As we know, other than LF, the starting defense will be made up of the same players again this season.

Next, Bummer had some poor luck in the batting average of balls in play (BABIP) department. The league average BABIP in 2023 was .297, while Bummer had a BABIP of .340 against him. Of course, BABIP is only a variable in a sea of many variables, but it is a variable none the less.

He also was extremely unfortunate in his strand rate. Only 55.4 percent of runners were left on base in 2023 for him. His career average is 69.1 percent. According to Fangraphs, the league average left on base percentage (LOB%) sits between 70.0 to 72.0 percent depending on the season. Before this past season, Bummer’s lowest rate was 64.5 way back in 2018 when he only pitched 31.2 innings.

A big reason for Bummer giving up the amount of earned runs is the amount of free passes he gave. His walk rate of 13.5 percent was the worst of his career and ranked in the bottom 4.0 percent of MLB. With his extremely low strand rate, it makes sense as to why his ERA was high. Odds are that over a larger period of time, his ERA would have dropped significantly.

If we look at Statcast we can see that his Expected ERA (xERA) was more than three full runs lower than his actual ERA. His xERA of 3.58 is much more palatable, and was in the best 24.0 percent in MLB in 2023.

If his insanely good groundball percentage of 60.1 percent (top 3.0 percent of MLB), mixed with his elite barrel percentage of 2.7 percent (top 1.0 percent of MLB) from last season can be maintained again in 2024, we can expect that his walks won’t hurt anywhere close to as bad as they did last season if his LOB bad luck wears off.

If you look at his profile, his walk rate is really his only major red flag. He has elite stuff. His strikeout rate was 29.2 percent last season (top 13.0 percent of MLB), and that was not an anomaly. Hitters struggled to make solid contact against him as well with an xBA of .218 and xSLG of .303 against him.

Let’s look at his arsenal

Bummer has a larger arsenal than most relievers with a mix of five pitches, but he relies heavily on his sinker (45.3 percent of the time in 2023), and his sweeper (38.0 percent).

As one can expect, he uses his sinker primarily in hopes of poor contact rather than strikeouts. His whiff percentage is low against this pitch at a 15.4 percent and his put away percentage is only 12.4 percent. That being said, the average launch angle against this pitch has been negative eight degrees or better every season since the start of 2019. According to Statcast, this is the pitch that hitters got a bit fortunate on with a slugging percentage of .452 against in versus an xSLG of .397.

His Sweeper has been nothing short of excellentsince 2019. As can be seen in the chart below his whiff percentage has been great for his entire career. Last season’s 44.8 percent was no fluke, and should continue in the future.

Sweeper Whiff percentage by season

Bummer likes to use this pitch as his put away pitch (pitch used on strike three) with it being affective 29.2 percent of the time in 2023. His rate has never dipped below 28.6 percent of the time (2019).

Based on his peripherals, and BABIP and LOB luck in 2023, it is no wonder why the Braves were interested in bringing in Bummer. Not to mention that he is a lefty RP option, which the Braves sorely missed last season.

Based on what we have looked at, Bummer could pitch exactly like he did last season and odds point to his end results having a positive regression to the mean. If this positive regression does happen, Bummer is going to be a welcomed addition to an already stacked Braves bullpen.

Not a single Bummer pun was made in this article. Sad.

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