It’s been a tough sophomore season for Royals reliever James McArthur.

After finishing the 2023 season strong as the Royals’ closer, it seemed like McArthur was due for a breakout campaign in 2024, especially with the Royals’ closing situation unclear initially after Will Smith’s early struggles.

McArthur showed some early promise but has struggled with consistency this season, especially in the second half.

Since the All-Star Break, McArthur has posted a 7.27 ERA in 17.1 IP, a far cry from the 3.99 ERA in 38.1 IP in the first half. His 4.39 FIP in the second half isn’t as bad as his 4.01 first-half FIP mark. That said, he’s been particularly hurt by an inflated HR/9 (1.56), a high BABIP (.385), and a low strand rate (52.4% LOB%) since the break.

As a result, the former Phillies draft pick has seen a decrease in high-leverage appearances, especially since the acquisition of Lucas Erceg at the Trade Deadline. However, in the few high-leverage situations McArthur has seen in the second half, he has failed to come through, which has drawn the ire of Royals fans frustrated with the inconsistency of the Royals bullpen this season.

It’s likely that McArthur won’t see many more closing situations this season, especially with his ERA at 5.01 for the year and Hunter Harvey due to return off the IL soon. However, that doesn’t mean the Royals should throw in the towel or designate him for assignment this offseason (which some Royals fans are suggesting).

With the right changes in his pitch mix this winter, McArthur could become a dependable reliever in 2025 and beyond who could be an excellent setup option with Harvey, John Schreiber, and maybe Daniel Lynch IV and Kris Bubic (should the Royals decide to keep them in the bullpen)

McArthur’s Struggles in High Leverage

A primary issue for McArthur this season has been his struggles in high-leverage situations, which is not what one wants to see from their closer.

Here’s a look at McArthur’s metrics in various leverage situations via Fangraphs:

McArthur has had some home run issues in low-leverage situations this year, as his 1.71 HR/9 illustrates. However, everything else has been solid.

In those lower-pressure outings, he has a 3.21 xFIP, a 19.3% K-BB%, and a 1.19 WHIP. Even in medium-leverage situations, the data is decent: 3.60 xFIP, 12.5% K-BB%, and 1.35 WHIP. The walk rate is a little high at 9.7%, but he makes up for it with a 22.2% K rate and 88.5% LOB%.

In high-leverage situations, the metrics become a little more discouraging.

Even though his K-BB% is serviceable at 12.7%, he has a high WHIP (1.70), BABIP (.393), and HR/9 (1.53). That unfortunate combo has resulted in a low LOB% (34.9%) and high FIP (4.54). In regular situations, those metrics are bad enough. In the most crucial parts of the game? They can be deflating.

Case in point? According to Win-Probabilty metrics via Fangraphs, McArthur leads all Royals relievers in “meltdowns” and ranks last in clutch.

McArthur ranks 2nd in “shutdown” appearances this year, behind only Schreiber, who has 22. However, the number of meltdowns he’s accumulated has negated all his positive outings this season. The only other Royals relievers with double-digit “meltdowns” this season are Will Smith and Angel Zerpa. Smith is currently on the IL, and Zerpa is in Triple-A Omaha.

Thus, it’s easy to understand Royals fans’ frustration with McArthur, especially since he has struggled so much in crucial late-inning moments.

On the other hand, while his struggles in high leverage are evident, that doesn’t mean he shouldn’t have a role in the bullpen in the future, especially after getting a full year of experience at the Major League level in 2024.

Looking at McArthur’s Pitch Mix and Quality

The overall metrics have been a bit disappointing for McArthur this year.

In addition to posting a 5.01 ERA in 55.2 IP, he has given up an HR/FB% of 16.7%, a 4.2% increase from a season ago. He also has seen a 5.6% decline in GB%, a 5.5% decline in K%, and an 8.2% decline in K-BB%. That has resulted in his fWAR going from 0.5 in 23.1 IP last year to 0.2 this season.

What’s interesting, though, is that there hasn’t been a tremendous decline in his pitch quality from 2023, especially on a PLV end. His curveball and sinker are still rated as above-average offerings, much like a year ago.

Last year, McArthur’s sinker had a 5.06 PLV, and his curve had a 5.71 PLV. This season? That sinker PLV is up to 5.29, and his curve is even better at 5.82. So, in theory, McArthur should be performing much better with his two primary pitches showing development, right?

Unfortunately, his slider, which he implemented when he joined the Royals organization, has dramatically declined this season. That trend has limited the effectiveness of his overall arsenal.

After posting a 5.43 PLV in 2023, his slider has only a 4.99 PLV this season, which ranks around the 20th percentile. When looking at both pitches individually, it’s interesting to see what pitch quality trends have contributed to the decline in PLV.

The slider has primarily declined in two areas: plvLoc+ (the modeled value of the pitch’s location) and the induced vertical break.

PlvLoc+ regressed from 112 in 2023 (12 points above average) to 99 in 2024, a 13-point decline. That demonstrates that McArthur isn’t commanding the pitch where he wants. Thus, hitters are taking advantage. He has seen his xwOBA against the slider go from .235 last year to .330 this season.

In terms of vertical break, McArthur’s slider has not been as sharp in terms of movement this season. Notice in the movement chart how more dots are above the x-axis this year compared to a year ago. That has resulted in more sliders hanging in the zone, yielding more production from opposing hitters.

Below is a clip compilation of sliders from the past two seasons. Notice how much more drop with the slider in 2023 compared to the one thrown back in April against the Mets.

The 2023 slider has more horizontal movement and drop, inducing Cleveland’s Myles Straw to chase, swing, and miss out of the zone. The 2024 slider generates a whiff from Joey Wendle, but it doesn’t have the same pitch quality as the 2023 slider. A better hitter would’ve done more with it.

Here’s an example of a better hitter doing more with a hung slider: Ian Happ of the Cubs back in a game at Kauffman on July 28th.

McArthur still has two excellent pitches in his arsenal: his sinker and curveball. The sinker’s put-away rate has increased this year, going from 15.4% in 2023 to 22% in 2024. Furthermore, the curveball has a whiff rate of 37.5%.

Unfortunately, McArthur will not be successful in the long term unless he improves his slider.

Adding a Cutter to the Mix in 2025?

Even though the curve has solid PLV metrics and a high whiff rate, it’s been hit harder this season.

According to Savant, he has a -3 run value on the pitch. In addition, his 45.5% hard-hit rate allowed on the pitch is a massive increase from the 19% hard-hit rate he had on the pitch in 2023.

The slider’s decline in quality has made it an ineffective pitch. Furthermore, it seems that it also affected his curveball results, which were dominant in 2023.

When looking at his pitch movement profile, it seems like the curve and slider don’t play well off each other, which makes it easy for opposing hitters to scout and tee off on both breaking pitches this year.

Notice how the curve and slider are in the same quadrant in 2023. That shows they sport similar and close movement, making it challenging for the opposing hitter to distinguish the two pitches. Furthermore, the 4.2 MPH difference only adds to the difficulty since hitters have less time to react, which results in either more whiffs or weaker contact.

This year, the pitches are in different quadrants, which makes it a bit easier to tell the difference between the slider and curve movement-wise. There also was a 0.2 MPH decline in velocity difference. That doesn’t seem like a huge change, but the combination of velocity and movement change has appeared to harm his breaking arsenal this season.

A solution to this problem could be McArthur adding a cutter to his arsenal in 2025.

Incorporating a cutter could be the bridge pitch between his sinker and his breaking arsenals. As seen in the induced movement profile of his arsenal this year, it’s easy for a hitter to distinguish between his fastball and breaking stuff due to the difference in movement. Having a cutter, a bit of an “in-between” pitch, gives another offering in his arsenal that makes him harder to scout.

John Schreiber is an example of a Royals reliever who effectively utilizes a cutter. Here’s a look at his induced movement profile and cutter movement and how they play off his sinker and four-seamer (which McArthur also throws).

As Royals fans can see, the cutter blurs things a bit for the hitter as that “bridge” pitch in between his sweeper (ST) and his four-seamer. It’s not perfect, as there’s more space between the cutter and sweeper than one would want. And yet, it’s been effective enough for Schreiber, especially since he doesn’t have a high-velocity fastball.

The cutter for McArthur could help bridge together his sinker and slider. In the clip compilation below, notice how Schreiber’s cutter would effectively complement McArthur’s sinker and slider, especially if thrown in the same area of the zone.

The slider in the third clip is called a ball to Ty France. However, if McArthur had a cutter in his arsenal, which was thrown hard and with less vertical movement, perhaps France would have chased that slider since, in theory, it would have a similar profile to his cutter.

In terms of stuff, McArthur is one of the Royals’ highest-upside arms. According to Fangraphs, he has the second-highest Stuff+ this season of any Royals reliever who is still on the roster and has accumulated ten or more IP.

As Royals fans can see, the only reliever he’s behind in Stuff+ is Carlos Hernandez, who’s had an underrated season after a disastrous second half in 2023. McArthur’s Stuff+ surprisingly rates better than Schreiber, Lucas Erceg, Hunter Harvey, and Kris Bubic, who have all been more embraced this season by fans than McArthur.

There is potential for McArthur to be a solid reliever at the Major League level, whether as a closer or not (a setup role feels a lot more realistic, especially with Erceg established as the closer and under long-term control).

He needs that tweak to the pitch mix to make him less predictable to opposing hitters.

Adding that cutter to his arsenal this offseason would be a step in the right direction.

Photo Credit: David J. Phillip/AP Photo