When the Royals acquired James McArthur from the Phillies back in early May, some Royals fans were wondering what JJ Picollo and the Royals front office were doing.

To acquire McArthur, the Royals gave up Junior Marin, a promising young outfield prospect who still had years of projection to go (though he had yet to progress past the Arizona Complex League prior to this season). Furthermore, Franmil Reyes, who offered some power potential to the lineup when he was acquired this offseason, was designated for assignment to make room for McArthur, even though McArthur remained a project who wouldn’t impact the Major League roster right away.

For a “rebuilding” club, a move like the one for McArthur is a necessary risk, even if it may seem unpopular with the casual baseball fan. After all, for small-market teams in the Major Leagues, finding and hitting on talent “overlooked” by other teams is key to long-term success.

If one wants to understand why teams like the Rays, Guardians, and even Orioles are successful, baseball fans (Royals fans especially) can check out those clubs’ rosters and see a lot of talent who were drafted/acquired by other teams but didn’t find success until they came to those respective small-market clubs.

In order for the Royals to find success like the Rays, Guardians, and Orioles in the next couple of years, Picollo and the front office need to find success stories from “under-the-radar” players, especially of the pitching variety.

The Royals tried to “develop” pitching talent from within (i.e. the draft and international signings) under Dayton Moore and unfortunately, it never quite worked out, especially after the Royals’ championship season in 2015. The failure to develop enough pitching, especially in the bullpen, ended up being one of the key reasons that cost Moore his position as the club’s president.

Granted, it hasn’t been the most sterling year statistically for the Royals pitching staff, especially bullpen.

The group ranks 28th in ERA, 27th in WHIP, 29 in BB/9, and 25th in H/9 and HR/9, which are all pretty lousy numbers. While the group does rank 12th in K/9, the Royals bullpen has seen a bit of regression in this category since Aroldis Chapman was traded away to Texas.

Despite the Royals’ struggles in relief, Kansas City has seen some unexpected production recently after the trade deadline. Jackson Kowar and Angel Zerpa pitching well as of late (due to changes in pitch mix and quality from a season ago). And though he has struggled since Scott Barlow was traded away, Carlos Hernandez remains a fireballer who can touch 100 MPH with ease and regularity.

That being said, all of those Royals relief stories pale in comparison to what McArthur has done over the past two months.

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Bouncing Back After a Rough Debut

I was able to be in person at the K for James McArthur’s debut on June 28th. And safe to say, it was difficult to watch.

In one inning of work, McArthur gave up seven runs on six hits and one walk. While McArthur did get a bit BABIP’d to death by a Cleveland lineup that is known for putting the ball in play, the command didn’t look good at all for the former Phillies pitching prospect.

Here’s a look at his pitch description chart from that debut outing, and notice how much McArthur missed in the middle of the plate (and what the Guardians did on those pitches).

Five of the Guardians’ batted balls in play against McArthur on those mistakes in the zone resulted in runs. That included this home run by Cleveland’s Bo Naylor on a 93 MPH sinker from McArthur.

Unsurprisingly, McArthur was demoted to the Minor Leagues shortly after the rough outing, with an MLB ERA of 63.00.

After taking some time to work on his command and stuff in the Minors (once again), the Royals called McArthur back up on August 4th (though they demoted him on August 17th), and then again on September 1st once rosters expanded.

Here’s a look at how McArthur’s monthly splits have looked this year, and notice how his numbers have looked since his lone rough outing in late June.

In five outings in August, things were still a bit rocky for McArthur as he posted a 7.50 ERA and 1.67 WHIP in six innings of work. While he did give up nine hits and five runs allowed, he did bump his strikeout total to four while keeping his walk numbers low (he had as many walks in five August outings as he did in one June outing).

Since his call-up in September, however, McArthur has been lights out on the mound for Kansas City.

In six outings and 8.2 IP, McArthur has allowed zero runs and walked zero batters while striking out seven and allowing only one hit. As a result of his stellar September, McArthur posted a 3.07 ERA and 0.75 WHIP in 11 post-All-Star Break outings.

Furthermore, on Monday, in the Royals’ 6-4 comeback win on Monday afternoon against the Guardians (the same team who tagged him for seven runs in his debut), McArthur earned his first career save by allowing zero runs and hits and striking out one on 17 pitches.

Here’s a look at McArthur’s pitch description chart from today’s outing.

Safe to say, based on the results of his pitches in the zone today, McArthur has come a long way since his June 28th debut against the Guardians.

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McArthur’s Pitch Quality (And Improved Command) Stands Out

McArthur sports a four-pitch mix, though it’s closer to a three-pitch mix based on usage.

He throws his sinker the most at 36.5% and follows that up with a curve which he throws 35.2% of the time and a slider which he throws 25.7% of the time. McArthur barely throws the four-seamer at 2.6%.

Here’s a look at the strike and plate discipline metrics of his four-pitch mix, via Pitcher List.

His breaking pitches have been particularly successful on both a SwStr% and CSW% end this season. His curveball is posting a 14.8% SwStr% and 33.3% CSW% and his slider is posting rates of 13.6% and 37.3% in those respective categories as well.

Here’s a look at McArthur’s curve and slider in action, as they generate whiffs from Houston’s Jeremy Pena and Seattle’s Teoscar Hernandez (more on this at-bat later).

The curveball is a more vertical-dropping pitch while the slider offers harder and more horizontal movement. It seems like hitters are having a harder time picking up McArthur’s curve, as opposing hitters are posting an O-Swing% of 42.2% which is 17.2% higher than the O-Swing% on his slider.

At first glance, the sinker doesn’t look like a great pitch, as it is only producing a CSW% of 25%. That being said, it looks a lot better on a PLV end, as Royals fans can see in the chart below.

McArthur’s sinker is producing a 4.98 PLV and a Q-BP% of 9.5%, which isn’t bad for a pitch that allows as much contact as it does. It’s also a plus that McArthur has a near-average main offering (average being 5) to go along with two excellent breaking offerings.

It also helps that McArthur has been able to sequence those three pitches nicely together this season, especially as of late. In the pitch chart below, notice where all three pitches fall in the zone on pitches that result in outs.

McArthur’s sinker averages 93.9 MPH so the near 10 MPH difference between this primary pitch and his two breaking pitches makes it challenging for hitters, especially if they are located in the same location.

In McArthur’s strikeout of Hernandez back at Kauffman on August 16th, he sets up Hernandez well by throwing a slider on an 0-1 count which gets him to chase out of the strike zone. On the next pitch, he finishes Hernandez off with a backdoor slider which Hernandez waves at late since he’s expecting a breaking ball but instead gets a fastball offering.

It’s that kind of three-pitch quality and command that could not just make McArthur a valuable reliever for the Royals in 2024, but perhaps a setup man or closer in the long term as well.

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Final Thoughts on McArthur

When it comes to Royals relievers in the month of September, no reliever has been better than McArthur in regard to FIP, according to Fangraphs.

Additionally, McArthur leads in ERA (0.00) and is tied for the lead among Royals relievers this month in fWAR (with Alec Marsh). His 2.95 xFIP is also only behind Taylor Clarke, who’s surprisingly been better since coming off the IL in September (Clarke is posting a 2.56 xFIP though his 8.31 ERA leaves a bit to be desired).

If that wasn’t enough, the 26-year-old former Ole Miss reliever is posting the best WPA/LI mark for Royals relievers this month. WPA/LI is also known as “context-neutral wins” and does a good job of measuring what a pitcher does in different situations.

It’s interesting to see that McArthur is not just the best reliever for the Royals in this category this month but Hernandez has been the worst. Thus, it’s not surprising that manager Matt Quatraro opted to go with McArthur for the save today rather than Hernandez.

Of course, this is just one month of play, and it’s possible that Hernandez is suffering from fatigue in his first full MLB season as a reliever (especially in a more high-leverage role). With a full offseason, could Hernandez be his mid-season self (which looked like a closer)?

As for McArthur, is this a flash in the pan or is he truly turning a corner to become the Royals’ closer for not just 2024 but perhaps beyond as well? The data seems to paint the picture that it may indeed be the latter.

Regardless of role, McArthur is proving to Picollo that he’s an arm that Picollo and the Royals can depend on for next season, as long as he’s healthy.

And that is a pitching development story that Royals fans can get behind, especially during a 100+ loss season.

Photo Credit: Reed Hoffmann/AP