In MLB.com’s most recent “holiday wish list” for all 30 MLB teams, Will Leitch said that the Royals needed “bullpen help” this off-season. Here’s what the former Deadspin founder (and noted Cardinals fan) said in his writeup on the Royals:

The Royals have been impressively aggressive so far, and the additions of Carlos Santana and Mike Minor really do make them look better. But a wobbly bullpen could tank everything they’re trying to do.

“1 holiday wish for all 30 MLB teams” by Will Leitch; MLB.com

The statement seems like a strange one, especially considering that the bullpen was a source of strength for the Royals in 2020. The Royals ranked 12th in reliever WAR, and 8th in reliever ERA last season, according to Fangraphs. In comparison, between 2018 and 2019, the Royals bullpen ranked 28th in WAR and ERA, according to Fangraphs metrics. Thus, to think that the Royals need to “improve” their bullpen first, when they still have some glaring needs in the lineup, seems like the typical “analysis” from an outsider who doesn’t really know the Royals organization as a whole.

However, while I disagree with Leitch that bullpen help is the Royals’ “primary” need this off-season (I still think another bat should be the priority; albeit an inexpensive one), I do think the bullpen will need an addition or two to make sure that 2020 wasn’t an aberration. While the Royals did bring back Greg Holland on a modest deal this Winter, Trevor Rosenthal, who was the Royals’ closer to begin 2020 until he was traded to San Diego, is still a free agent, and it’s difficult to tell whether or not the Royals will bring him back, especially since he will be more expensive than Holland. Furthermore, while the Royals had breakout seasons from Josh Staumont, Kyle Zimmer, and Jesse Hahn last year, all three have a history of struggles with injury and/or control, and it is possible that one or more of that trio will see regression in 2021, especially over a full 162 game season.

Thus, it is likely that the Royals will add another reliever or two before Spring Training, though any targets will probably be similar in mold to Holland and Rosenthal got a year ago (i.e. one-year MinorLeague deals initially). That could bring some interesting options to Kansas City, such as possible reunions with former Royals relievers Wade Davis and Kelvin Herrera, who both are free agents, and could merit such Minor League contracts.

However, an overlooked option who could boost the bullpen may be Jakob Junis, who most likely will be shifting to the bullpen after the acquisition of Mike Minor this off-season.

Because if recent history should serve as precedent for the Royals, then Junis may be the next former, struggling starter to thrive in the Kansas City bullpen.

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The Royals have had some decent success converting mediocre Major League starting pitchers into valuable bullpen assets in the last decade.

In 2013, the Royals moved former No. 1 pick Luke Hochevar to the bullpen, and saw him improve in many categories across the board. In 58 appearances and 70.1 IP, Hoch posted a 1.92 ERA; improved his K/9 from 6.99 to 10.49, and his K/BB ratio from 2.36 to 4.82; and increased his whiff rate from 8.7 to 13.4 percent, according to Fangraphs. The following season, Wade Davis made a similar move to the bullpen from the rotation and also saw similar gains, according to Fangraphs metrics: a 1.00 ERA (from 5.32 in 2013 as a starter); 13.63 K/9 (from 7.58 in 2013); 4.74 K/BB ratio (from 1.97 in 2013); and 14.3 whiff rate (from 7.3 in 2013).

Furthermore, even recent examples of Royals starters moving from the rotation have for the most part been successful. In 2019, Ian Kennedy, who had combined for a 1.0 WAR across 52 starts in 2017 and 2018 combined, became the Royals closer and thrived in the role. In 63 appearances, Kennedy saved 30 games, posted a 3.41 ERA and 1.5 WAR, and also improved his K/9 (from 7.90 to 10.37) and K/BB ratio (from 2.63 to 4.29) from 2018 to 2019, respectively. And last season, Jesse Hahn, who mostly pitched as a starter in San Diego and Oakland, before arriving to Kansas City, became one of the Royals’ best relievers, as he posted a 0.52 ERA and 0.5 WAR in only 17.1 IP.

Thus, it isn’t crazy to think that Junis can be another Hahn or Kennedy, or even Hoch or Davis in a best case scenario. After a solid first couple of seasons that saw him post an ERA of 4.30 and 4.37, in 2017 and 2018, respectively, Junis has seen his ERA inflate to 5.24 and 6.39 in 2019 and 2020, respectively. One of the big problems with Junis has been giving up the long ball. According to Fangraphs, his HR/FB rate has risen to 16.7 and 25.0 the past two seasons. Though Junis demonstrates good control (he sports a career 3.32 K/BB ratio), his lack of an ability to keep the ball in the yard has been concerning for Royals fans, and limits his potential as a starter in the Royals rotation.

However, what Junis does possess is pretty elite potential on one pitch: his slider, specifically. In 2019, according to Statcast data, Junis’ slider was the 11th best slider in baseball in terms of Run Value. Of pitchers who faced 100 or more batters, his 44.4 percent strikeout rate on the pitch was seventh best in baseball, ranking higher than sliders of more well-known pitchers such as Trevor Bauer (who ranked 8th in K rate), Brand Hand (who ranked 9th), and Noah Syndergaard (who ranked 10th), according to Statcast rankings. Ben Palmer of Pitcher List also posted this Tweet below last March, showing the effectiveness of Junis’ slider in 2019.

Because I miss baseball, I'm gonna start doing a series of random pitchers with really good pitches.

First up today, one of my favorite pitches around, Jakob Junis' slider, it's like a frisbee

– 34% chase rate
– 14.4% SwStr rate
– .239 wOBA against
– 14.5 pVAL pic.twitter.com/CWgBelEFtb

— Ben Palmer (@benjpalmer) March 17, 2020

However, Junis did see some regression with his slider in 2020, though the weird season, and him missing time due COVID, probably didn’t do him any favors. His slider only had a run value of zero, but it was still his most effective pitch in terms of whiff rate (26.7 percent), K percentage (27.7 percent), and wOBA (.308), according to his Statcast metrics. Furthermore, the slider was the most utilized pitch in his arsenal, as he threw it 46.2 percent of the time, which was much higher than his 29.6 percent slider usage in 2019. Hence, the increased usage probably had an effect, as hitters saw it nearly twice as much from Junis in comparison to years past.

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So, if Junis’ slider effectiveness regressed, that can’t be a good sign for him in the bullpen, right? Well not exactly.

The one positive trend that Kennedy, Davis, and Hoch all saw was a dramatic increase in their fastball velocity in their move from the rotation to the bullpen. Kennedy’s fastball increased from 91.9 MPH in 2018 to 94.5 to 2019; Davis’ fastball increased from 92.1 MPH in 2013 to 95.7 MPH in 2014; and Hoch’s fastball increased from 92.6 MPH to 95.5 MPH from 2012 to 2013, respectively. The only one who didn’t see an increase was Hahn, who saw some spot time as a reliever for the Royals in 2019, but he did increase his fastball velocity from 93.8 in 2017 while as a starter in Oakland to 95.1 MPH in 2019 (though that increase was probably due to Tommy John surgery recovery rather than just a straight move to the bullpen).

All these former Royals converted starters saw an increase in velocity in their fastball because they could let loose more now that their innings and pitch counts were far less as relievers. And thus, if all four of those former Royals pitchers saw increases of around 2-3 MPH in fastball velocity, the same could be true of Junis, which could make his fastball, a pitch of weakness for him lately, more effective. Junis did see his run value on his fastball drop from 12 to 0 from 2019 to 2020, so a 2-3 MPH increase in 2021 could not only make his fastball more effective, but also help his slider get back to those elite levels of 2019.

The Royals will need an effective bullpen to succeed and climb in the AL Central standings in 2021. While Rosenthal would be a nice return for the Royals pen, even a couple of Minor League lottery tickets could also be worthwhile, especially since GM Dayton Moore has seen some recent success with such a strategy. That being said, while many Royals fans may think “external” options will be the key to the Royals bullpen continuing to progress as a unit in 2021, it may be their “internal” options that will either make or break their season in 2021.

And Junis is one of those “internal” candidates who could really turn the tide for the Royals next year. If Junis is able to see a tick on his fastball and be able to utilize that as an effective pitch again to go along with his slider, not only will his arsenal be more successful in 2021 out of the bullpen, but he could also become a long-term option for the Royals as a reliever for the next couple of seasons after 2021 as well.