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Breaking Down Keynan Middleton

Keynan Middleton had a mini-breakout in 2023 following an overhaul of his pitch usage.

New York Yankees v Chicago White Sox Photo by Brandon Sloter/Image Of Sport/Getty Images

The St. Louis Cardinals have made another foray into the free agent market snagging an affordable relief arm to deepen the bullpen. Keynan Middleton signed for 1-year and $6 million with a team option for the 2025 season worth $5 million after spending last season with the White Sox and then joining the Yankees at the trade deadline.

The obvious attraction here is the strikeout rate. Middleton missed bats at a 30.2% rate en route to posting a 4.20 FIP and 3.26 xFIP. That may not be extraordinary but it does constitute a mini breakout for Middleton. Yes, I’m saying this about a pitcher worth 0.1 fWAR last year but I promise I’m not crazy. That’s why I’m not calling it a full-on breakout.

Look at it this way. Middleton posted the best ERA of his career post-COVID, the second best FIP of his career behind only a season in which he threw just 17 innings, and the best xFIP of his career while setting career best marks in strikeout rate and ground ball rate.

It’s those last two things that I want to focus on now because it’s clear that Middleton didn’t just improve in 2023; he became a completely different pitcher.

Let’s start with his Fangraphs page to provide some perspective.

The pitcher I see in 2023 doesn’t look anything like the pitcher I see in 2017-2022 and there’s one clear reason for that

The Pitch Mix

Middleton made an intentional change to his pitch usage that completely changed his profile last year.

Middleton has always been a fastball-dominant pitcher. Well, until last year that is. And by “fastball-dominant” I mean that his fastball usage dominated the usage of his other pitches. What I don’t mean is that his fastball dominated hitters because that couldn’t be further from the truth.

In 2021, when Middleton was throwing his fastball 57.7% of the time, hitters posted a .397 wOBA against it. He dipped his fastball usage to “just” 50.6% the following year and hitters responded by crushing it to the tune of a .486 wOBA. The pitch simply wasn’t good.

Now I want to stress my word choice here. Note that I said “wasn’t” and not “isn’t”. That’s because the pitch was, in fact, good in 2023. It generated a .234 wOBA and a 33% whiff rate.

That last number is where things get interesting because you would think the high whiff rate is a large reason why the pitch was so successful (and you would be right). The thing is that Middleton’s fastball also generated whiff rates above 30% in each of the two prior years.

So it’s weird. Middleton’s fastball is good until it’s not. It misses bats until it doesn’t. And then when it doesn’t, it gets crushed. I’ll have more on that later.

So what does a pitcher do when his fastball is getting crushed? He throws it less. Like a lot less. In fact, only 5 pitchers (min. 400 pitches) threw fastballs at a lower rate than Middleton. Instead of pitching off his fastball, the hard-throwing right-hander is now hiding it to great effect.

The interesting thing is that he basically replaced his fastball usage with his changeup usage. Now the changeup, which is typically a change of pace offering, is Middleton’s primary pitch and his fastball has become the change of pace offering.

Middleton’s fastball can really change the pace too. The pitch travels at 95.5 mph and has a perceived velocity of 96.3 mph due to Middleton’s ability to generate well above average extension towards the plate.

So, as a change of pace offering, the fastball appears to be just fine. Better than just fine actually. It seems to be a pitch that can truly be an effective part of Middleton’s arsenal. We’re obviously looking at just a one year sample of 225 fastballs but it’s encouraging nonetheless.

What’s also encouraging is that Middleton’s changeup was still effective with expanded usage. That’s the sign of a positive change and it’s the expanded changeup usage that really tuned Middleton into a new pitcher.

Which of his pitches has the highest whiff rate? His changeup. Which pitch get the most ground balls? His changeup. Which pitch has the highest chase rate? His changeup. And which pitch gets thrown in the zone the most? Also his changeup.

So how did Middleton have a career best strikeout rate and nearly double his ground ball rate at the same time? The answer is simple. He threw more changeups.

This is a crucial pitch for him and the way that he had success with it is unorthodox. For starters, he threw it in the zone a ton. That’s unusual. His 56.1% in-zone rate was well above the 39% league average in-zone rate on changeups.

Changeups are primarily a chase pitch. They are thrown down and away outside the zone to opposite handed batters in an effort to induce chases, whiffs, and weak contact. That’s where they thrive.

So the level of success that Middleton had with in-zone changeups is unusual. League-wide, in zone changeups aren’t bad. They generated a .321 wOBA and 21.9% whiff rate in 2023 which is fine. Solid even. The difference is that out of zone changeups generated a .246 wOBA and a 44.4% whiff rate. That’s much better and it explains why pitchers use their changeups as a chase pitch.

Middleton, though, was able to generate a .278 wOBA and 29% whiff rate when he took his changeups in the zone. Those are well above average results and, quite frankly, he needed to have well above average results in this regard.

If Middleton is going to use his changeup as his primary pitch, he can’t just leave it outside the zone all the time; he needs to be able to get consistent strikes with it. So the fact that the pitch plays well in the zone allows him to be more aggressive with it.

So that’s the first way Middleton is unorthodox with his changeup usage - he throws his changeup in the zone a ton and it works for him.

The second way that he is unorthodox with his changeup usage is that he throws a ton of same-sided changeups. In fact, only 3 relievers threw more same-sided changeups than Middleton in 2023.

Over 52% of Middleton’s changeups were thrown against right-handed batters. That’s unusual and it’s not a strategy that pitchers tend to follow. Why is that?

There’s two reasons. Changeups tend to run reverse splits, meaning that a right-handed changeup tends to get better results against left-handed batters than against right-handed batters (this actually wasn’t true in 2023 and that is something that may warrant further investigation). Still, though, changeups aren’t bad same-sided offerings.

So the real reason why pitchers tend to avoid same sided changeups is opportunity cost. If you’re throwing a same-sided changeup then you’re not throwing a same sided breaking ball and breaking balls tend to show much stronger splits in the normal direction.

Let me illustrate the point. In 2023, batters put up a .286 wOBA against right-on-right changeups. That’s good, right? Well, against right-on-right breaking balls, hitters put up just a .274 wOBA. That dropped to .257 against sweepers.

There are generally more effective pitches to use than changeups when pitchers have a platoon advantage so pitchers tend to really limit their changeup usage and use breaking balls instead.

Not Middleton, though. The slider is Middleton’s go-to pitch against right-handers but only just barely. He threw 202 right-on-right sliders last year compared to 191 right-on-right changeups. Middleton doesn’t pocket his changeup like other pitchers do when they have the platoon advantage. Rather he throws is boldly as his primary in-zone weapon (51.8% in zone changeup rate against RHBs).

Keynan Middleton is just plain weird and he leans into it.

But did it work? It’s one thing to be weird but it’s another thing to be effective. Sometimes those things work together and sometimes they don’t. So really the question is twofold. How did Middleton’s same sided changeups fare and were they more effective than his same sided sliders?

Last year, the answer to the second question was yes. Middleton’s changeup performed better in right-on-right situations than his slider. The changeup not only allowed a lower wOBA (.332 compared to .356) but it also posted a higher whiff rate (42.5% compared to 37.8%).

So Middleton’s weirdness is good. Or, rather, it was good in 2023. Keep in mind that we’re looking at a reliever and we’re aren’t dealing with the largest of sample sizes. So let’s get a bigger sample size by looking at Middleton’s career numbers.

Keynan Middleton Career R/R Sliders vs Changeups

Pitch # of Pitches wOBA Whiff Rate Pitcher Run Value/100
Pitch # of Pitches wOBA Whiff Rate Pitcher Run Value/100
R/R Changeup 248 0.316 42.80% -0.3
R/R Slider 767 0.271 37.50% 1.1

When we take a longer term view with a larger sample size we see that Middleton’s slider has played better than his changeup against right-handed hitters. I know the 2023 data is different but I’ll bet against the smaller sample size and stick with the general trend and Middleton’s career trend. What I’m saying is that he’s probably better off sticking to his slider against righties and dialing back his changeup usage in those scenarios.

As it turns out, that’s exactly what the Yankees had him do after they traded for him last year.

Here what his pitch usage against right-handers looked like last year, broken up by month:

This is the pitch usage that I favor. You can see how Middleton’s slider overtook his changeup in the last two months of the season after he was traded to the Yankees but his changeup didn’t just go away. He still used it to right-handers, he just turned it into much more of a secondary offering.

This isn’t clear cut, though. Remember when I mentioned that Middleton throws an unusually high number of changeups in the zone? Well it turns out that he doesn’t do the same thing with his slider. That’s why he can use his changeup as a primary pitch and that’s why the idea of him using his slider as his primary offering is a little sketchy.

Middleton threw only 33.2% of his sliders in the zone in 2023 and that didn’t improve when he started using his slider more. So that’s really the next area of improvement for him and his pitch usage is going to depend on whether or not he can put his slider in the zone at will.

If he can’t, then he probably does need to stick with a changeup heavy approach against right-handed batters.

Final Thoughts

I’m glad the Cardinals dove back into the reliever market. Middleton is another interesting arm that can miss bats and has a newfound ability to keep the ball on the ground. He does have a history of arm injuries and walks so there is some risk with him but at 1-year and $6 million there’s not much.

The Cardinals have done a great job of assembling a large group of interesting relievers at a relatively low cost and the Middleton signing is just another way of adding depth and competition to the bullpen.

I skipped over this earlier in the article because I really wanted to focus on the pitch mix changes that Middleton made which allowed him to spike his strikeout rate and his ground ball rate but the righty also had a crazy high 23.5% HR/FB rate last year. That’s crazy high.

That high of an HR/FB rate is due for regression and that could work wonders for Middleton even if he can’t bring his walk rate down or throw his slider in the zone more often.

So we’re looking at a pitcher who reinvented himself in 2023 but still has multiple to improve next year. Better slider control would lead to more walks but good old fashioned batted ball luck could help him build on his mini breakout in 2024 and help him add value to the Cardinals bullpen.

Thanks for reading, VEB.