Baseball Analytics: Aaron Bummer to Be One of the Best?

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The Apparent Importance of Relievers

With cost of top tier relievers in baseball sky rocketing (LHP Aroldis Chapman signed a 3 year / $48mil contract with the New York Yankees and RHP Liam Hendriks signed a 3 yr/ $54mil contract with the Chicago White Sox) MLB front offices appear to acknowledge the necessity of quality relievers.

The White Sox were able to dish out so much money to Liam Hendricks knowing they had a steal coming by signing the 558th pick in the 2014 draft LHP Aaron Bummer to a 5 year / $16 million contract. This deal buys out two of his arbitration years plus a three year extension with the club as well as a team option for 2025-2026. The contract makes him the 48th highest paid reliever in baseball while teammates Craig Kimbrel and Liam Hendricks rank in the top 5.

Stats That Stand Out

Some may ask why a reliever with a 3.51 ERA in 56.1 innings pitched should be deserving of any more money than what he already received.

There are a few stats that stand out in his 2021 season. The main one that stands out is a 121 ERA+. ERA+ is a stat that accounts for ERA of play as well as stadium and league conditions. Stats like ERA+ make it easy for people to obtain information about a player, as the league average is 100.

Aaron Bummer’s 121 ERA+ indicates that he was 21% better than the average pitcher. I believe that number is only going to get bigger.

When you dive into some of the advanced analytics you see his true potential to be one of the best.

Advanced Analytics Hint at the Potential

From Bummer’s baseball savant page you would believe he may be one of the best relievers of all time. His pitch mix and velocity is impressive as he has an above average fastball at an average of 95.4 while still being able to get up to 98.9. He also posses a slider which he threw 30% of the time in 2021 which is his money pitch and I will explain more on why later. He also likes to mix in a cutter 8% of the time. As we move on to the next section, I will break down what each individual stat means and why it’s important.

The first one that stands out is xSLG, i.e. expected slugging percentage. According to, this “is more indicative of a player’s skill than regular slugging percentage, as xSLG removes defense from the equation. Hitters, and likewise pitchers, are able to influence exit velocity and launch angle but have no control over what happens to a batted ball once it is put into play.”.

Aaron Bummer was in the 100% percentile in this stat meaning he was the best in the entire MLB in the 2021 season. He also ranks above the 95th Percentile in five different statistical categories. One that may be slightly more significant than the xSLG is that he was in the 99th percentile for Barrel %. This can be quite easy to understand: if a pitcher is one of the best at avoiding barrels of the bat, that is going to lead them to more success. According to Baseball Savant, Aaron Bummer only allowed 2% of his balls in play to be barrels. This is insane to hear as the MLB average is around 7%! As a result of him avoiding so many barrels, it allows him to get many ground balls. He ended 2021 with 75.4% of all his balls in play being groundballs. It’s a lot harder to hit homeruns when they only go 5 feet. 

Why is he so hard to hit? The Sinker and The Slider.

While yes, it already is hard enough to hit a lefty throwing 95+, some reasons why he’s even harder to face come down to pitch movement and sequencing. The average movement of a sinker to a right handed batter is a horizontal movement of 15 inches and a drop of 23 inches. Bummer’s sinker comes in moving 16 inches horizontally and an impressive 29 inch drop!

Now we get to what I refer to as his money pitch: his slider. It moves 18 inches towards a right handed batter with a drop of 46 inches. The MLB average on a slider is 6 inches horizontally and a 37 inch drop; Bummer significantly passes each one of those. 

As you can see from the graph above, his slider was trashed for a little while. But, in 2020, it began to make an increase. In 2021, it shot up from a usage of 5.8% to 29.6%.

In that 2021 season, he threw his slider 282 times and only was hit 8 times for a .095 batting average! Another crazy statistic about Aaron bummer slider is that it had a Whiff percentage of 52.2. This means that on all swings, more than 50% of the time they don’t even make contact with the ball, which again is an affect of his ability to miss barrels.

The graphic above shows which pitch he throws in which counts. One thing Bummer does really well is getting ahead in the count using his sinker as he has a first strike percentage of 57.2% in 2021. Even in what are considered to be even counts, he still attacks with the sinker because he understands the importance of putting the batter in scenario where they have to protect. The reason he attacks this way his because he knows he only throws his slider for a strike 35% of the time so his plan is to attack hitters and get them behind in the count and then put them away with the devastating slider.

The White Sox Bullpen Is Now Even Stronger

Aaron is in quite a lucky scenario as he has some of the greatest relievers of this era on his team to help him develop and pick the brains of Liam Hendricks and Craig Kimbrel. The Chicago White Sox have one of the best bullpens in baseball and because of signings like this and others made it’s only going to continue to improve. When you take the top five relievers out of this bullpen, Micheal Kopech, Aaron Bummer, Liam Hendricks, Garrett Crochet, and Jose Ruiz, you get an average ERA+ of 118.6.

Hot take there is a chance that by the end of next year Aaron Bummer becomes the best reliever in this bullpen.

I will never be upset at a player for taking a deal like this. Bummer, a 558th overall pick coming out of the university of Nebraska, is only getting a signing bonus of 100,000 dollars. During his first three years in the MLB he only made $1,639,000. This contract not only gives him and his family some financial security for the rest of their life but also gives him security in years of doing what he wants. Often times, during contract negotiations players get more concerned about the amount of years they’re signed to the contract more than the average annual value (AAV). Overall this is a really great deal for both parties especially favoring the White Sox as they have the possibility to get one of the best relievers in the league at a steal of 2.5 million dollars a year.

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