Despite second half struggles, Royals fans should be hopeful about Jake Brentz in 2022

While the Royals starting pitching staff went through their fair share of ups and downs during the 2021 season (they ranked 24th in team ERA and 27th in WHIP), the bullpen was at least a little better, even if it did see some regression from the 2020 season. After ranking 8th in bullpen ERA during the COVID-affected 2020 campaign, the Royals bullpen ranked 19th this year in reliever ERA and 16th WHIP. Even though that is not a sign of an “elite” bullpen by any means, it’s at least promising considering the Royals finished 74-88 in 2021.

After all, even a slight improvement in the bullpen could go a long ways in terms of helping the Royals improve overall in the Win-Loss column next year.

The Royals at the least have a solid, “closer” in Scott Barlow, who not only generated 16 saves in 71 appearances, but also posted a career-best 2.42 ERA and 2.1 fWAR in 74.1 IP, according to Fangraphs. After Barlow, however, the Royals have some promising, though inconsistent and/or unproven options slated to be in the Royals bullpen in 2022. Josh Staumont wasn’t pumping the 100 MPH stuff as often in 2021 as he did in 2020, but he did post a 2.88 ERA and 1.0 fWAR in 65.2 IP last season. Furthermore, Domingo Tapia, picked up for cash considerations from the Mariners, ended up being one of the Royals’ most dependable relievers down the stretch, as he posted a 2.84 ERA in 32 IP and 31 appearances for Kansas City last season.

However, one of the more polarizing relievers in the Royals bullpen last year was Jake Brentz, a 27-year-old rookie and product out of the St. Louis metro area (he went to Parkway Central High School) who was acquired from the Pirates organization back in 2019.

Brentz turned all kinds of heads in Spring Training, and made the Opening Day roster over other left-handed options such as Richard Lovelady and Gabe Speier, much to the surprise of many Royals fans. However, to begin the year, Brentz produced on the mound immediately, as he posted a 1.86 ERA in 9.2 IP in the month of April and a 2.40 ERA in 15 IP during the month of May. After the first two months of play, it was widely thought among Royals fans that Brentz could not only be a key arm in the late innings during the remainder of the 2021 season, but also could be an affordable and valuable relief option long term for the Royals as well.

Unfortunately, things turned for Brentz later in the season, especially after the All Star break. After posting a 2.95 ERA in 39.2 IP in the first half of the season, Brentz posted a 4.81 ERA in 24.1 IP in the second half of the season, according to Fangraphs splits data. While Brentz still posted an ERA under 4 (3.66 to be specific), he only finished with a 0.2 fWAR, which is only SLIGHTLY above replacement level. In addition, his HR/FB rate (13 percent) and much higher xERA (4.39) and FIP (4.23) than his ERA also belie that Brentz may have been a beneficiary of some “luck” on the mound last season, which isn’t good for his outlook in 2022.

And yet, when diving deeper into his metrics, there are some areas where Royals fans should feel encouraged about Brentz. If he can make some modifications in mechanics to improve control and command, it is possible that Brentz could have an even bigger breakout in 2022, and perhaps emerge as the Royals’ second-best reliever behind Barlow.


One of the biggest issues that Brentz has struggled with over his professional career has been control. Even during his Minor League career, Brentz has only posted a walk rate under 10 percent twice in his career: with the Naturals (the Royals’ AA afiliate) and the Altoona Curve (the Pirates’ AA affiliate) in 2019.

This season, his struggles with control surfaced again, as he posted a 13.3 percent walk rate for the year in his MLB debut. Even during his strong months of April and May, he still had his issues with finding the strike zone. In April, he posted a 12.2 percent walk rate and K/BB ratio of 2.20, which isn’t great, but not bad by any means. However, in May, his walk rate spiked to 18.5 percent, and his K/BB ratio dropped to 1.20, both significant regressions in control.

That being said, how did Brentz find success during those early months despite his issues finding the strike zone?

Well, Brentz was either benefiting from the Royals defense, getting lucky, or honestly, experiencing a combination of both. That shows in his BABIP and strand rates (LOB %).

In April, hitters posted a BABIP of .240 against Brentz, and in May, that BABIP was .139. That was further amplified by strand rates of 72.7 percent and 92.6 percent in April and May, respectively. While the April strand rate is typically around average, the 92.6 percent isn’t, and when combined with a ridiculously low BABIP and subpar K/BB ratio, it was only a matter of time before things caught up with Brentz, which is what happened later in the season.

The strand rates especially took a hit after May, as he posted rates of 68.5 percent in June, 66.7 percent in August, and 45.5 percent in September/October. Granted, his July rate was pretty high (80.7 percent), but for the most part, after May, Brentz was not as fortunate when it came to avoiding hits and keeping base runners on, two important keys to success for a Major League pitcher, especially one who pitches in relief.

On the other hand, while the ERA spiked in the second half, one could argue that Brentz’s advanced metrics showed an improved pitcher, especially when it came to control, his biggest issue prior to 2021.

In the first half of the season, Brentz posted a 15.4 percent walk rate and 1.73 K/BB ratio, both mediocre marks. In the second half, Brentz lowered his walk rate to 10.1 percent and increased his K/BB ratio to 2.82, both significant gains. Furthermore, he also increased his strikeout rate from 26.6 percent in the first half to 28.4 percent in the second half, and his FIP actually went DOWN from 4.33 in the first half to 4.07 in the second half.

Brentz did give up the long ball more in the second half than the first half (0.91 to 1.11) and he experienced major regressions in BABIP (.207 to .317) and LOB % (79.3 to 61 percent). However, Brentz was modeling a much better process and approach on the mound in the second half, even if the results didn’t really come to fruition during the latter part of the 2021 season.

Thus, what can Brentz do this offseason and Spring to help him generate a more “consistent” 2022?


Two things Brentz does pretty well is that he generates a high percentage of groundballs, and he also can pile up strikes both on a swinging and called strike basis. I did some analysis of Royals relievers who threw 30 or more IP in 2021, and check out where Brentz ranks among that category of Royals pitchers, according to Fangraphs:

As Royals fans can see, only Zimmer had a higher groundball rate than Brentz. On the flip side, Brentz generated less hard hit contact than Zimmer, as Zimmer posted a hard hit rate that was 1.3 percent higher than Brentz. Of Royals relievers with 30 or more IP, only Tapia posted a lower hard hit rate than Brentz, which is a good sign for Brentz going forward. Groundballs are preferable for any pitcher, as Max Greenfield on Twitter reiterated and correlated with teams who were successful this past season:

From a relief end, generating groundballs can make or break a reliever at the MLB level. Groundballs can lead to double play outs, and the ball isn’t going out of the park either. However, one interesting thing to note about Brentz that makes him atypical to some groundball-inducing pitchers is that he can pump the velocity on pitches, as he ranked in the 94th percentile in fastball velocity, according to Baseball Savant. In addition, he also showcased an above average ability to generate strikes, as evidenced by his CSW (called strikes plus whiffs) rate via Fangraphs:

Only Barlow posted a better CSW rate than Brentz, and that isn’t a surprise considering that Barlow was worth over two wins this past season on a fWAR basis. That is promising to see, especially considering 2021 was Brentz’s rookie debut at the Major League level.

Brentz has the tools to make progressions toward being a Barlow-esque reliever, as generating groundballs and throwing strikes at a high rate are two qualities that Brentz and Barlow share. In addition, Brentz has a solid four-pitch repertoire (four-seamer, slider, changeup, and sinker) that could make him an effective option in the late innings in 2022 and beyond, as evidenced from Baseball Savant run value data:

As Royals fans can see, Brentz has been effective with the four-seamer, as he is posting a minus-four run value on the pitch, even though his whiff rate on the four-seamer is much lower than the slider and changeup. While his slider is his best pitch on a whiff rate (43.2 percent) and K rate end (36.4 percent), he also made a lot of mistakes with the pitch that ended up hurting Brentz dearly this past season. Even though he threw his slider far less (27.9 percent) than his four-seam fastball (58.4 percent), he gave up two more home runs on his slider (4) than his four-seamer (2) in 2021.

And a big problem with his slider was consistency of command on the pitch, especially on batted balls.

Take a look at Brentz’s heat map when he threw sliders that were batted for base hits this past season:

That’s right in the heart of the zone, and hitters are going to take advantage, as Bobby Bradley of Cleveland did to help the Indians to a walk off victory at Progressive Field back in July:

Now, let’s take a look at Brentz’s heatmap when he was able to use his slider to generate outs, whether it was through strikeout or field outs in 2021:

When Brentz was able to keep it low in the zone, he proved to be an effective reliever and keep opposing hitters at bay.

Take a look at Brentz getting Byron Buxton, arguably the Twins’ best hitter, to swing and miss on a slider from Brentz that is thrown right in the deep red dot area back in September at Target Field:

Thus, when Brentz is commanding his slider, he cements his place as the Royals’ second-best reliever behind Barlow going into Spring Training in 2022. That being said, he can’t be making those mistakes up in the zone with the pitch next year, or else hitters will continue to feast with big hits next season, just like they did especially in the second half this past year.


While Brentz throws his four-seam fastball a majority of the time, his slider is his most effective pitch, and has the most upside long term. That is made even more evident when one compares their Statcast metrics on the pitch.

Here’s a look at the data on his four-seam fastball this year:

And now, let’s take a look at his Statcast data on his slider from 2021:

Brentz showed better control with his slider than his fastball (five walks to 28 on his fastball) and was much better in terms of striking batters out on the slider (36 percent K rate) in comparison to the four-seam fastball (22 percent K rate). The only issue with the slider was the long ball (1 percent HR rate on the fastball to 5 percent HR rate on the slider), and that honestly was mostly due to command of the slider, not necessarily the quality of the pitch.

It is possible that Brentz simply wore down at the end of the season, which affected the command of his slider down the stretch. Brentz missed time at various points during the second half of 2021, which makes sense considering this was his first full professional campaign since 2019.

Unlike Zimmer, who wore down spectacularly in the second half of the year, Brentz still was demonstrating some promising metrics despite the lackluster results, which is further shown in many of his positive percentile rankings via Savant:

Many Royals fans may be sleeping on Brentz for next season due to recency bias, which makes sense considering that he was more “rough” than “impressive” at the surface level in the second half. It will be more common for Royals fans to talk about Dylan Coleman or Tapia, especially considering how they finished the year on more positive notes. They are the more “shiny” relievers, especially considering they didn’t pitch as many innings as Brentz did last year.

That being said, there are a lot of good aspects about Brentz’s profile from 2021, and that shouldn’t be ignored among Royals fans. With some adjustments in command this offseason, and with a full season at the MLB level already under his belt, it is possible that Brentz could be one of the Royals’ top-three relievers in 2022 and maybe beyond, should he stay healthy.

Photo Credit: Peter Aiken-USA TODAY Sports

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