The Royals pitching staff has been an adventure this season, and that’s putting it lightly. While we know about the Royals’ starting pitching struggles this season beyond Cole Ragans, the bullpen has arguably been just as bad if not worse in 2023.

This is disappointing considering the flashes of promise Dylan Coleman and Taylor Clarke demonstrated a season ago, as well as the early success of Carlos Hernandez, who looked like the Royals’ best reliever beyond Aroldis Chapman before Scott Barlow was traded away.

For the season, the Royals’ bullpen ranks 29th in ERA and BB/9, 27th in WHIP, and 25th in HR/9, according to Fangraphs. Granted, the group has collected a fair share of strikeouts, ranking 11th in the league in K/9. Unfortunately, the strikeout ability of the bullpen has been the lone positive takeaway from this group this season.

Even though it’s been a disappointing season for the bullpen, and the individual numbers of Royals relievers don’t look great either, there still are some positives to glean with this group, especially from the younger relievers who are starting to gain a footing at the Major League level.

Let’s take a look at three pitchers, who most likely are relievers at this point in their careers, who have shown some progress this season both at the Major and Minor League level and are worth paying attention to down the stretch.

Even though their surface-level metrics aren’t great, they have shown some potential with a particular pitch that could help make the rest of their repertoire better with a full offseason and spring of development under the Royals pitching development team.

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Jackson Kowar and the Slider

Kowar has long been a polarizing pitching prospect in the Royals system.

Once thought of as having the most upside of that 2018 Draft class which included Brady Singer, Daniel Lynch, Kris Bubic, and Jon Heasley, Kowar has struggled to earn a permanent spot on the Royals’ pitching staff over the past three seasons. Even though Kowar has long sported a plus changeup, his mediocre fastball and breaking offerings have long prevented him from being successful at the Major League level.

This season, he made the transition to the bullpen, and as expected under the new pitching development team, he worked on tweaking his pitches, particularly his four-seamer and slider.

The changeup has continued to be a solid offering, as it is producing a 24.7% CSW for the season, according to Pitcher List. In addition, his four-seamer has improved from producing a 25.% percent CSW rate in 2022 to a 29.7% mark in 2023.

However, on a CSW and PLV end, his slider has been his most impressive offering and is a big reason why his 4.42 FIP is 2.05 points better than a season ago.

As of Thursday, Kowar is producing a 17.1% swinging strike rate and a 33.3% CSW rate with his slider, which ranks him in the 64th and 72nd percentile in those categories, respectively. The swinging strike rate is 10.4% better than a season ago, and a big reason for that increase is that the slider is generating more chases this season than it did in 2022.

Last year, Kowar’s slider only generated an O-Swing% of 17.6%. This season? That slider is producing an O-Swing% of 36.6%.

That shows that the breaking pitch is sporting a better quality than a season ago, and that is evident in the PLV data this year, as his slider sports the best PLV and PLA of his three offerings.

Let’s look at his slider from 2022 and 2023 in the clip compilation below.

In 2022, Kowar’s slider was more of a looping offering that only averaged 83.1 MPH. Thus, it was easier for batters to lay off of it when it was thrown out of the zone once they picked up the spin.

This season, the slider is averaging 85.9 MPH and it’s a much sharper and harder-dropping pitch. That makes it tougher for hitters to lay off of it when it’s thrown on the edges, as was the case in Kowar’s strikeout of Pittsburgh’s Liover Peguero at Kauffman Stadium on August 30th.

As a result of a better-quality slider, Kowar has thrown the breaking offering much more regularly this season. He’s throwing the pitch 25.4% of the time this season, which is a huge spike from both 2021 and 2022.

The changeup will continue to be a solid pitch for Kowar at the Major League level. That said, he’s showing that his slider can be just as good a pitch, which makes him a reliever with intriguing potential for the Royals in 2024.

If he can hone his four-seamer a bit more (while the CSW is impressive, the PLV demonstrates that the pitch quality still needs work) it’s possible that Kowar could be one of the Royals’ more dynamic relievers next season.

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Angel Zerpa and the Sinker

Injuries have derailed Zerpa in 2022 and 2023 so it’s important that Royals fans take his 6.11 ERA with a grain of salt.

While Zerpa did post a 1.64 ERA a season ago, it was only over 11 innings, and his 5.70 xERA and 4.89 xFIP demonstrated that he probably got lucky during that small sample.

On the flip side, his xERA this season is 5.27 and his xFIP is 4.36. That shows that it’s been a bit of an inverse season in terms of batted-ball luck, which should make Royals fans hopeful that Zerpa can turn it around in 2024 with some batted-ball regression.

A big difference for Zerpa this season has been that he’s utilizing his four-seamer less and his sinker more as his primary fastball pitch, which can be seen in his year-by-year pitch chart, via Savant.

After throwing his four-seamer nearly 60% of the time in 2021, he’s lowered its usage to 33.2% this season. Conversely, he only threw the sinker 7.4% and 9.4% of the time in 2021 and 2022.

This year? That sinker usage rate is 20.9%.

Now on a swing-and-miss end, the sinker isn’t a great pitch.

The four-seamer is producing a 17.1% whiff rate, which isn’t great but is nearly double his 8.5% whiff rate on the sinker. That said, while the sinker lacks “whiff” potential, its 29% CSW rate is 5.7% better than the CSW of his four-seamer, and on a PLV basis, the sinker has been a far better pitch as well.

As Royals fans can see, Zerpa’s sinker is 0.48 points better on a PLV end, and 1.47 points better on a PLA end as well. In fact, his sinker is his second-best pitch on a PLV end, behind only his slider, which is posting a 5.13 PLV this year.

Frankly, the fact that his slider is his best pitch in terms of PLV could be a reason why Zerpa is throwing his sinker more. It complements his slider a lot better than his four-seamer in terms of movement and location, which can be seen in the clip compilation below.

After seeing a gradual rise in sinker usage with each outing, Zerpa relied more on his four-seamer in his most recent appearance on Tuesday against the White Sox, which can be seen in the game-by-game pitch usage chart via Savant.

It will be interesting to see if Zerpa will go back to using his four-seamer more, or if this was just a blip on the radar based on matching up with an aggressive-swinging White Sox lineup.

Regardless, which fastball offering Zerpa utilizes more at the conclusion of 2023 could give a glimpse into what kind of pitch arsenal Zerpa will employ overall next season.

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Steven Cruz and the Four-Seamer

Cruz had a disastrous MLB debut on August 29th as he gave up four runs on three hits and three walks in 0.2 IP.

Since then, the results have been much better, including his “opener” outing against the White Sox on Wednesday as he struck out four, walked zero, and allowed two hits and zero runs in two innings of work. Here’s also how his exit velocity and CSW numbers looked against the White Sox on September 13th as well, via Savant.

Cruz relied on his sinker a bit more in this outing and his slider was a more effective pitch on a whiff end on Wednesday. However, his four-seamer may be the pitch to watch from Cruz long-term.

On a CSW end, the four-seamer is only producing a 20% mark, which is pretty minuscule and not a promising sign for future success.

On the other hand, a big issue is that he’s struggled to control the pitch at times, despite its premium velocity. As a result, Cruz has seemed to focus on throwing the pitch with more control and command, even at the expense of velocity.

Here’s a look at his pitch velocity chart on his four-seamer via Savant, and notice the downward trend since his MLB debut against the Pirates.

In terms of PLV, there’s not enough data just yet to get a full picture of Cruz’s four-seamer, but it’s been up and down in terms of quality so far in 2023.

Here’s a look at his PLV metrics from his Sept. 9th and 4th outings and notice how wildly different his four-seam PLV is in those respective outings.

Against the White Sox, Cruz’s four-seamer was humming with a 5.41 PLV. Unfortunately, he was nearly two points worse the following outings against the Blue Jays on a PLV end (and I’m sure the drop in velocity didn’t help).

Let’s take a look at how his four-seamer looked in his first outing against the Pirates and how it has appeared recently in his September 4th appearance against the White Sox.

At first glance, it seems like his four-seamer has more vertical/rising movement against Pittsburgh, while the four-seamer against Chicago has less vertical movement and more horizontal movement.

Based on his average horizontal break chart via Savant, it seems like Cruz may be trading less vertical movement for a greater amount of horizontal break on the four-seamer.

That explains the trade-off in velocity, as pitch velocity typically correlates with more rising vertical movement (which four-seamers are known for). While Cruz is sacrificing velocity, he’s also limiting walks as a result, which I’m sure he would rather have in his first MLB stint.

Nonetheless, it will be interesting to see the direction pitching coach Brian Sweeney and director of pitching performance Paul Gibson will push Cruz toward this offseason when it comes to his four-seamer and pitch repertoire in general.

Will he get the vertical movement back on his four-seamer and help him harness his control so he can utilize it for whiffs like Hernandez?

Or will they perhaps push him to use his sinker more so he can have better control and command, even at the expense of strikeouts like Zerpa?

Hopefully, the Royals coaching team can find an outlook in the middle with Cruz, starting in 2024.

Photo Credit: AP Photo/Charlie Riedel