What's Going On With Lucas Erceg?

There have been plenty of problems with the 2026 Kansas City Royals. After all, they wouldn't be 8-17, tied for the worst record in baseball, if they didn't have flaws. That said, the Royals' bullpen has been a glaring weakness, significantly contributing to Kansas City's struggles through its first 25 games this season.

According to Fangraphs, the Royals' relievers rank 30th in ERA, 29th in WHIP, 28th in H/9, and 27th in BB/9 and HR/9. On a positive note, they rank 14th in K/9, which is better than a season ago (they ranked 29th in 2025). Unfortunately, they have seen major declines in every other statistical category.

On an individual basis, many important Royals relievers have struggled in the above-listed categories, including SIERA, which is the acronym for Skill Independent Earned Run Average. Here are the definition and formula for SIERA, according to MLB.com. 

Quote

Definition
SIERA quantifies a pitcher's performance by trying to eliminate factors the pitcher can't control by himself. But unlike a stat such as xFIP, SIERA considers balls in play and adjusts for the type of ball in play.

For example, if a pitcher has a high xFIP but has also induced a high proportion of grounders and pop-ups instead of line drives, his SIERA will be lower than his xFIP.

The formula
6.145 - 16.986(SO/PA) + 11.434(BB/PA) - 1.858((GB-FB-PU)/PA) + 7.653((SO/PA)^2) +/- 6.664(((GB-FB-PU)/PA)^2) + 10.130(SO/PA)((GB-FB-PU)/PA) - 5.195(BB/PA)*((GB-FB-PU)/PA)

 

SIERA can be a good indicator of a pitcher's skills this year, like FIP. However, SIERA does a much better job of accounting for grounders and pop-ups, which are more favorable for a pitcher. 

Here's a list of Royals relievers and their advanced metrics this season, as organized by SIERA.

Some Royals relievers have been solid this year, based on SIERA. Daniel Lynch IV and Alex Lange have SIERA marks under three, which is encouraging. Matt Strahm has a SIERA of 3.63. That's not great for his standards, but it's much better than his 5.19 ERA and 5.57 FIP. 

Conversely, one reliever who has struggled this season is Lucas Erceg, who has taken over closer duties in Kansas City since Carlos Estevez landed on the IL after his lone appearance in Atlanta during Opening Weekend. 

Erceg ranks 10th of 12 qualified Royals relievers in SIERA with a 5.95 mark. That is much worse than his 5.79 ERA and 4.32 FIP. Only John Schreiber (6.16) and Mitch Spence (7.05) have been worse this season in SIERA (and Spence has only made one appearance at the MLB level). 

When looking at Erceg's numbers this year, he's been pretty poor across the board. His 4.82 K/9 ranks 11th, his 6.75 BB/9 is 4th-highest, and his 0.71 K/BB ranks 10th. He hasn't given up a home run this season, but that's been the lone positive for Erceg on the mound this season. 

So what has been the issue with Erceg this season, especially after being so locked down in the closer role in 2024 when he came over at the Trade Deadline? That season, Erceg posted an 11.16 K/9, 1.08 BB/9, 10.33 K/BB, and 2.26 SIERA in 25 IP. He also had 11 saves that season and was a key part of their bullpen in the postseason.

Erceg does have five saves this season, but he's already blown two games in 10 appearances, the same number he blew in 23 appearances in 2024. 

Thus, let's look more deeply into Erceg's profile, what the issue has been, and whether he will be able to correct it at all this season to help improve this struggling bullpen unit.

Examining Erceg's Statcast Percentiles from 2024 to 2026

A good place to start with Erceg is looking at his TJ Stats Statcast summary from the past three seasons. That could give us a full picture of Erceg, not just in terms of his ability to generate strikes, but also his stuff and ability to avoid hard-hit batted balls. 

Here's a look at his 2026 TJ Stats Stacast summary through 10 games.

When looking at his Statcast percentiles this year, Erceg is a bit of a conundrum.

On one end, he's still flooding the strike zone and generating groundballs. His 44.9% zone rate ranks in the 73rd percentile, and his GB% of 51.8% ranks in the 79th percentile. Additionally, his fastball ranks in the 92nd percentile at 97.5 MPH, and he doesn't have a pitch under the 101 TJ Stuff+ mark.

However, when it comes to batted-ball metrics and strike data, Erceg has been incredibly lackluster. 

The 30-year-old reliever ranks in the 15th percentile with a 91.1 MPH average EV, 35th percentile in hard-hit rate with a 44,4% rate allowed, and in the 49th percentile in barrel rate at 7.4%. Thus, while he's producing a good number of groundballs, he's also allowing a fair number of hard-batted balls that are doing damage. That is evidenced by his .362 xwOBA (25th percentile) and .356 xwOBA (23rd percentile). 

The strike metrics are even more concerning.

Erceg ranks in the 7th percentile in K% and BB%, 6th percentile in whiff%, 4th percentile in O-Swing%, and 1st percentile in CSW%. He's also allowing a ton of contact in the zone, as evidenced by his 87.7% Z-Contact%, which ranks in the 23rd percentile. Erceg is not just failing to generate strikes or swing-and-miss, but inducing chase. All those characteristics have made him a mediocre reliever in 2026,

Now, let's take a look at what he did in 2024, when he was with the Athletics and Royals. 

In 61.2 IP with the A's and Royals, Erceg pretty much excelled in every category. That includes K% (87th percentile), BB% (81st percentile), CSW% (89th percentile), O-Swing% (76th percentile) and Z-Contact% (85th percentile). Those were all categories where Erceg ranks below the 10th percentile this season.

One could argue that Erceg was one of the most talented and underrated relievers in baseball in 2024, and it makes sense, given that, why the Royals acquired him at the Trade Deadline. That said, his Statcast percentiles looked a little different in 2025 in his first season with the Royals.

The fastball velo, GB%, and BB% remained table last season. However, he began to show signs of regression across many key areas. His CSW dropped to the 33rd percentile, his K% dropped to the 35th percentile, and his Z-Contact% dropped to the 43rd percentile. The O-Swing% was still solid, ranking in the 66th percentile. The same could also be said for his barrel% allowed (61st percentile) and hard-hit% allowed (70th percentile).

That said, Erceg began to show flaws last season across so many Statcast metrics, and perhaps this regression was to be expected given that trend (though maybe not as dramatic or as soon).

What's the Deal With the Swing and Miss?

For a reliever to succeed in the ninth, they have to be able to generate swing-and-miss, especially in those high-leverage situations. It's hard for a closer to be successful long-term if they're not able to produce whiffs and strikeouts in the ninth.

In 2024, Erceg had a 31% whiff rate and 28.7% K%. In 2025? That whiff rate fell to 24.7%, and K% regressed to 19.4%. This year, he's really bottomed out in those two categories, with a 16% whiff rate and 12.8% K%.

Below is a trend of Erceg's swing-and-miss% over his career. Notice how it dropped sharply last season, especially after a decent start to 2025. 

After finishing with a Swing-And-Miss% in the 32.5% range, he bottomed out last year, with his Swing-And-Miss% even dropping to under 10% just past the 600th swing mark. This year, his Swing-And-Miss% is hovering around the 17.5% mark. While that's not as bad as what it got to at the end of 2025, it's not a promising sign, especially so early in the season. 

To understand Erceg's whiff problem, it may be helpful to look at his overall repertoire and how each pitch has fared this season.

Here's a glimpse of Erceg's arsenal profile, via TJ Stats. 

It doesn't seem to be a stuff problem for Erceg, at least according to TJ Stuff+.

He has an overall mark of 103 with two of his pitches (sinker and changeup) sporting 60+ grades. His four-seamer, his most thrown pitch, has a 101 TJ Stuff+ and a 56 grade. However, despite those encouraging metrics, he just isn't able to get hitters to miss. His overall whiff rate is 16%, and he's generating a 13.3% whiff rate on the four-seamer (as well as a 14.3% chase, which isn't good either). 

Now, let's look at his TJ Stats season summary from 2024.

The four-seamer and overall stuff profiled better in 2024 with a 104 TJ Stuff+ on the four-seamer and 106 TJ Stuff+ overall. That said, his whiff rate in 2024 absolutely blew away his 2026 mark. In 2024, he had a 31.2% overall whiff% and a 28.6% whiff% on the four-seamer. Those elite metrics explain why Erceg was utilized as a closer and fireman down the stretch in 2024 for the Royals.

Now, let's take a look at his 2025 TJ Stats summary.

A lot regressed for Erceg last season. The TJ Stuff+ was 102 overall, and his four-seamer actually had a TJ Stuff+ mark under 100. However, he still generated a 28.2% whiff rate with the four-seamer, only a 0.4% difference from his 2024 four-seamer whiff rate. 

Thus, it may be that Erceg's four-seamer is the difference this year. However, if it's not a stuff problem (his four-seamer TJ Stuff+ is better this year), it must be a command issue, which may be a tougher fix.

The Four-Seam Location Hasn't Been Good

This season, not only is Erceg just generating a 13.3% whiff rate, but he is allowing a .595 xwOBACON on the four-seamer this year. That has contributed to only poor fastball results (zero run value, according to Savant), but lackluster overall numbers as well.

That said, I don't think it's a "stuff" issue with his four-seamer. His 101 TJ Stuff+ on the four-seamer this year is actually two points better than what he did last year. And yet, his whiff rate on the pitch is 14.9% lower than a year ago. 

Thus, the problem is likely due to his inability to command the four-seamer effectively. 

A good way to test this hypothesis is to examine his heatmap data on TJ Stats. That could give a sense not just of the heatmaps for lefties and righties on the pitch, but also of the metrics.

Here's Erceg's four-seam heatmap this season.

Erceg has thrown the four-seamer a fair amount against lefties (38.9%) and righties (31.9%). It has also gotten hit around by both sides of the plate. 

Against lefties, Erceg's four-seamer is producing only an 18.9% CSW% and allowing a .601 xwOBACON. Against righties, he's generating a 13% CSW% and .571 xwOBACON. When looking at his heatmap, it's easy to see why Erceg is failing to generate strikes and allowing a lot of hard hits: he's throwing the pitch way too much in the strike zone. 

For context, let's look at his four-seam heatmap data a season ago.

Erceg seemed to elevate the four-seamer better last year, especially against lefties. Notice how the bright orange circle is closer to the top of the strike zone than the one in 2025 against lefties. Closer to the top of the zone is good for four-seamers, especially ones with Erceg's velocity. 

As a result, the former Cal product generated a 33% CSW% and .379 xwOBACON against lefties and a 28.2% CSW and .393 xwOBACON against righties. The numbers weren't as good against righties, but he also didn't elevate the ball as consistently against righties as he did against lefties last season.

Here's an example of Erceg elevating the four-seamer effectively last season against Cleveland's CJ Kayfus to generate the swing and miss.  

Erceg not only throws it 98 MPH, but he locates it up and away in the zone, even in a 2-1 count, which tends to favor the hitter. That shows the confidence and feel Erceg had for the fastball last year. 

Now, let's take a look at a fastball thrown by Erceg to Baltimore's Samuel Basallo. Erceg grooves this in the middle of the zone on a 1-2 count (which favors the pitcher), and the Rookie Orioles catcher hits in the gap to help Baltimore tie the game (they later relinquished the lead).  

In order for Erceg to generate whiff and effectiveness with the four-seamer, he has to get command of the pitch again. A start would not just be to throw it for strikes, but get to throwing it up in the zone, especially against lefties, which he was effective at doing last season. 

Final Thoughts on Erceg

Right now, Erceg isn't pitching well by any stretch of the imagination. His ERA, BB/K ratio, and SIERA demonstrate that. However, with Estevez on the shelf, Erceg continues to be the Royals' best option in the ninth.

I say that not because of the results, but because the TJ Stuff+ numbers remain promising for Erceg. When looking at the TJ Stuff+ leaderboard for Royals pitchers via TJ Stats, Erceg ranks third in overall TJ Stuff+ with a 103 mark. He's behind only Steven Cruz (109) and Nick Mears (105). 

There are many issues that Erceg needs to correct. His 24.4% zone rate on the slider has to improve, as it is 15% lower than it was a season ago. It's easy for opposing hitters to lay off Erceg's primary breaking pitch when he's not even locating it in the strike zone 25% of the time.

However, the four-seam command needs to be priority number one for Erceg and Royals pitching coach Brian Sweeney. If Erceg keeps grooving it in the middle of the zone, it's going to continue to get hit hard. If he's able to locate it more up in the zone, he can keep hitters honest, which could open up his other offerings, especially his changeup and slider (if the latter can be controlled more effectively). 

Sweeney has been lauded for his staff's work with the Royals pitchers over the past couple of years. Now, the Royals' bullpen, especially Erceg, needs to understand and correct these issues soon in order to turn around the club's fortunes for the remainder of the season.

If Sweeney can't help Erceg, or any other members of this bullpen, not only will wins become tough to acquire, but Sweeney may find himself in a hotter seat than expected by the conclusion of the season.