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The Resurgence of Keynan Middleton

by Thatcher Zalewski

Keynan Middleton was signed to a minor league contract by the White Sox on January 15, 2023, mostly brought in to be depth in Charlotte and fill out the Knights’ roster. The reliever received an invite to big league camp, but failed to make the Opening Day roster. By all accounts, he was looking like just another everyday reliever signing that most teams go through in the final months of the offseason.

Middleton was promoted to the White Sox on April 10 due to an injury to relief pitcher Joe Kelly. Many fans thought that Middleton would just be there as a low-leverage reliever and just fill a spot in the bullpen until Kelly returned. This was because in 2022 Middleton finished with an ERA of 5.29 in 18 games, with his best days with Los Angeles seemingly far behing him (his last season of solid success was in 2019).

However, Middleton proved himself in the bullpen almost immediately by striking out three of the four batters he faced in his debut. Since then, he hasn’t looked back and has proven himself as a high-leverage arm in the White Sox bullpen.

In 30 innings this season, Middleton has posted the highest strikeout rate of his career (31.7%) while posting an incredibly solid ER A(2.70), FIP (3.62), and xFIP (2.84).

So, what changed? How did Middleton turn his career back to 2019 in his first 30 games with the White Sox?

Well, we will be exploring that today.

Pitch Selection

One of the big things that is contributing to Middleton’s success is the change he made in his pitch selection. This year Middleton has made his changeup his primary pitch while putting the fastball in the backseat. Middleton has thrown his changeup 42.2% of the time this year whereas in 2022, he only threw it 17% of the time.

Now if we go back to 2021, where he had more of a consistent presence in the Mariners bullpen, Middleton only threw his changeup 12.1% of the time in 32 games. Middleton’s changeup usage is at a career-high, as he’s never thrown it over 100 times in a season besides this year.

Throughout his career, Middleton’s changeup has always been his best pitch in terms of whiff rate. So, this first change is just a case of throwing his best pitch more often. Hitters are batting just .191 off of his changeup, with an xBA of .221 showing that the pitch is indeed working as intended.

This change in pitch mix has also made Middleton’s other pitches more effective. For example, Middleton’s fastball has become a legitimate put-away pitch for the first time in his career. Middleton currently has a PutAway% of 31.8% with his fastball, which is a career-high for him. Previously, the highest it has ever been was 24.2% back in 2022. Middleton’s Whiff% on his fastball this year is at 36.2%, which is another career best for him. The slider has pretty much always been Middleton’s secondary pitch for him throughout his career. This year though, Middleton has seen an increase in his Whiff% and PutAway% on his slider. In 2022, Middleton had a 40.0 Whiff% and a 17.6 PutAway% on his slider. In 2023, Middleton currently has a 44.8 Whiff% and a PutAway% of 23.9%. It doesn’t appear Middleton has made a change in pitch shape to his slider, either – this is simply a case of pitch mix and velocity doing the work.

In short, Middleton’s ability to gain more whiffs and use his fastball and slider as put-away pitches have been a big part of his turnaround this year. Instead of relying on the fastball as his primary pitch with the changeup and slider as secondary and third pitches, he is now relying on the changeup more which has made him much more effective on the mound.

Batted Ball Profile

Another big change for Middleton this year is the ability to limit fly balls and line drives. Due to this change, Middleton has seen a spike in his ground ball percentage – likely in part to his increased changeup usage.

Every single one of Middleton’s pitches has seen an increase in ground balls from 2022. His fastball and changeup have seen a bigger increase than his slider, however, these differences are important. Middleton’s GB% saw the largest change as it rose from 11.5% in 2022 to 30.8% in 2023. This is the highest GB% Middleton has had on his fastball since 2017, which was at 32.5%.

His changeup has seen the second-highest change in GB%. As of 2022, Middleton had a GB% of 55.6% to 69.7% in 2023. The last time Middleton came even close to matching this number was again in his rookie year back in 2017. However, he only threw his changeup 18 times and used it almost exclusively against left-handed hitters. This goes back to the first big change for Middleton in making his changeup his primary pitch.

Lastly, Middleton’s slider has seen a small change in GB% from 2022. So far Middleton is at 42.1% with his GB%, while in 2022, Middleton had a GB% of 40%. This isn’t a very drastic difference, but it does show that Middleton is becoming more effective with his pitches.

Taking a look at Middleton’s LD% (Line Drive Percentage) there are two notable decreases. Middleton has seen an increase on his slider though. However, let’s first look at the fastball and changeup percentages.

The biggest change does come with his changeup, which he has made his primary pitch, having the largest decrease in LD% from 2022. In 2022, Middleton’s LD% on his changeup was 33.3% and in 2023 it is currently at 18.2%. The last time it was this low was in 2021 when it was 14.3%, but Middleton didn’t throw it nearly as much as he has so far in 2023. This has led to Middleton seeing almost a career-best in exit velocity on his changeup.

His fastball has also seen a drastic change. This year Middleton has a LD% of 23.1% on his fastball, but in 2022 he had a LD% of 34.6%. The last time Middleton had a LD% this low was in 2019 when it was at 16.7% which was a career-best. This has benefited Middleton in the launch angle department. It is currently a career-best for Middleton at 14 degrees, which explains the increase in GB% and decrease in LD%.

Middleton’s slider has seen an increase in LD%, however, this is in part to Middleton using it more as a put-away pitch which was touched upon earlier. This slight increase for Middleton hasn’t had much effect on many of his statistics, so there is not a whole lot to touch on.

One of the last things we will touch on is Middleton’s barrel percentage. Middleton is currently at a Barrel% of 7.7%, which is his best since 2020 when he sported a Barrel% of 2.8%. Middleton’s ability to limit barrels has helped him limit the hard contact he gives up. This plays a big part in him only allowing three home runs this year – one of which was a swing like this.

Taking a look at his Barrel% pitch breakdown, the biggest difference comes with his fastball. Last year in 2022, Middleton’s fastball was at a career-high Barrel% of 23.1%. This year Middleton is at a Barrel% of 15.4%, which is in part to him making his fastball a secondary pitch rather than his go-to pitch.

Middleton’s changeup and slider have seen increases in Barrel%. This is in part to him using those two pitches more than he has in previous years. It goes back to the whole idea of making the changeup his primary pitch.


Middleton has done a lot to right his path and may have found a home in Chicago. These were just a few of the things that needed to be highlighted to show off his drastic changes. It is always great to see guys like Middleton turn the page and have success with the big league club.

This just goes to show that spending the big bucks on the bullpen may not always be the best idea.

Follow us @SoxOn35th for more throughout the season!

Featured Image: Kamil Krzaczynski-USA TODAY Sports

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