The unlikely breakout arm giving his team a timely lift

Just as they did last year, the Royals are winning on the backs of a stalwart rotation: Entering play on Sunday, Kansas City's starting pitchers had combined for a 2.63 ERA, the second-best mark in baseball.

What’s surprising, though, is that there’s a new face leading the way.

Kris Bubic, a 27-year-old left-hander, has been the best of the bunch. Through his first nine starts, Bubic ranks fifth among qualified starting pitchers with a 1.66 ERA and eighth with a 2.70 FIP. He’s allowed just one run in his last 18 innings, heading into Monday night’s start against the Giants in San Francisco.

With Cole Ragans and Seth Lugo landing on the injured list over the weekend, Bubic's importance has only grown.

This isn’t some overnight success story. Bubic’s transformation started three years ago, coming off his third big-league season -- in which he went 3-13 with a 5.58 ERA for the 97-loss Royals. The 40th overall pick in the 2018 MLB Draft, Bubic was at an early crossroads.

“I don’t consider myself the same pitcher now [from] those first three seasons,” Bubic said after an eight-strikeout performance against the Orioles on April 6. “My pitch mix is a lot different. My delivery is a lot different. … It’s wild to think about how it’s all come together.”

What’s happened since is a testament to modern pitching development. After the 2022 season, the Royals cleaned house, bringing on Brian Sweeney and Zach Bove to overhaul their pitching department, with a refined focus on analytics.

Bubic had to wait a little while to fully reap the benefits, as an elbow injury ended his ‘23 campaign after just three starts. Tommy John surgery followed, and Bubic went nearly 15 months without climbing a big league mound. He returned last July as a reliever -- in a pennant race -- and flourished, instilling confidence in the organization that he could still be a starting pitcher. After winning a job in Spring Training, he hasn’t looked back.

“We knew coming into the season that [Bubic is] a pretty darn good guy pitching the fourth day of the season for us,” Royals manager Matt Quatraro said on March 31, after Bubic tossed six scoreless innings in his season debut.

But this good? Maybe not. Let’s take a closer look at the changes fueling Bubic’s breakout start.

All stats below are through Saturday.

A rising 4-seamer

The story of Bubic’s transformation begins with his four-seam fastball.

Bubic isn’t a hard-thrower. His four-seamer has an average velocity of 92.3 mph, which ranks in the 21st percentile of MLB. And yet, only seven qualified starting pitchers induce a higher whiff rate with their four-seamer than Bubic (31.3%). Of that group, six throw their fastball at an average velocity of 95.6 mph or faster.

Highest 4-seam fastball whiff rates, SP
Min. 50 swings vs. 4-seamers (139 qualifying pitchers)

1. Tarik Skubal (DET): 34.9% (97.6 mph)
2. Zack Wheeler (PHI): 33.7% (95.6 mph)
3. Luis L. Ortiz (CLE): 33.3% (96.1 mph)
4. Bryan Woo (SEA): 33.2% (95.6 mph)
5. Hunter Brown (HOU): 33.1% (96.1 mph)
6. Garrett Crochet (BOS): 32.8% (96.0 mph)
7. Michael King (SD): 31.6% (93.7 mph)
8. Kris Bubic (KC): 31.3% (92.3 mph)

In his last start on Tuesday against the Astros, Bubic topped out at 95.3 mph with his four-seamer. The pitch generated a career-high 13 whiffs on 25 swings, running a 52% whiff rate. How does he do it?

For one, the pitch has exceptional ride. Bubic is averaging 18.5 inches of induced rise on his four-seamer, 2.4 inches more than the average left-handed pitcher. Essentially, he spins the baseball in a way that allows the pitch to resist gravity on its way to the plate. Hitters expect the pitch to drop, but it drops less than they anticipate, and they wind up swinging underneath it.

There’s another layer of deception at play here, too. Typically, “rising” fastballs are thrown by pitchers with over-the-top arm angles, who have an easier time putting backspin on the baseball. But Bubic induces rise from a low arm slot, at 38°. Standing at six-foot-three, his release height (5.69 ft.) is actually a tick beneath the league average.

“To be able to get the above-average carry from that below-average release point has helped the angle be flat, even at 92, 93 (miles per hour),” Bubic told MLB.com Royals beat reporter Anne Rogers in April. “The swings still tell me that guys are behind it, not squaring it up, not seeing it.”

That wasn’t the case three years ago, when Bubic’s four-seamer posted a -31 Run Value -- by that metric, the least-valuable pitch in baseball. Batters hit .348 against the pitch. That’s on par with their slugging percentage (.361) against Bubic’s four-seamer this season.

Bubic's 4-seamer, 2022 vs. 2025

2022: 91.9 mph / 2,134 RPM / 16.5" induced rise / 7.7" arm-side run
2025: 92.3 mph / 2,404 RPM / 18.5" induced rise / 4.9" arm-side run

Often, a shape change stems from a grip change -- as we’ll see later with Bubic’s changeup. But Bubic has maintained a standard four-seam grip with his fastball. He credits heightened “intent” behind every pitch, as well as improved health, for the renaissance.

“Going through 12+ months of elbow rehab has allowed me to put a bit of cleaner spin on the ball, because my elbow feels better and is probably a little bit stronger than it was previously,” Bubic said in April. “My theory is, I’m able to better apply force to the baseball and spin it a little better.”

Better secondary offerings

Added spin helped Bubic develop an elite fastball. The opposite is true with regards to his changeup -- killing spin created a pitch with more drop.

“I used to throw a changeup on the four-seams,” Bubic said. “It was kind of feast or famine. You get a guy way out in front, but it’s a hard pitch to land in the zone because it just ends up being a slow fastball.”

We can see what Bubic is talking about by looking at his pitch movement charts for 2022 and 2025. Three years ago, there was little movement differential between his four-seamer and changeup -- just an 11 mph velocity gap between the two pitches. Bubic, in his words, was just trying to “pull the strings” to fool hitters. The green circle shows the movement on Bubic's changeup; the red circle is his four-seamer.

Notice the sizable amount of separation between the two pitches this year -- a stark difference from '22. As a result of a grip change, Bubic's changeup now drops 4.4 inches more than comparable changeups, thrown at similar velocity and release point.

“Having more depth than it has in the past, it’s gonna be a more consistent weapon,” Bubic said. “Especially if the fastball has the life that it has, pairing the changeup off of that, riding that pair.”

The fastball/changeup pairing is only a piece of the puzzle: Against left-handed hitters, Bubic throws his changeup just 2% of the time, instead turning to a pair of new breaking balls. He developed a slider in ‘23, first threw a sweeper in ‘24, and is now using both pitches this season, completely shelving his curveball. With a diverse five-pitch mix (he throws a sinker, too), Bubic can make smarter, platoon-based pitch decisions, which he couldn’t do with a limiting three-pitch mix across his first three MLB seasons.

That's helped unlock another level of dominance. Lefties have gone from a .372 BA/.611 SLG combination against Bubic in '22 to a .222 BA/.333 SLG line through nine starts in '25.

A new mentality on the mound

New pitches and better shapes are great, but there’s something else going on here, too.

In his relief cameo last season, Bubic attacked hitters in a way that he seldom had before. To date, he's maintained that attack-first mindset as a starting pitcher.

Bubic's aggression

2020-22: 50.2% Zone% / 55.7% 1st Pitch Strike% / 10.5% BB%
2024-25: 54.2% Zone% / 62.8% 1st Pitch Strike% / 5.9% BB%

The mindset paid off for Bubic last summer, when he pitched to a 2.67 ERA with an 11.6 K/9 ratio as a late-inning reliever. While his role has changed, he approaches each inning the same way.

“Instead of being like, ‘Hey, you’re going to throw six or seven innings today,’ it’s almost like, ‘Hey, go be a reliever for one inning and then do it again, do it again, and do it again.’ Breaking the game into smaller parts has made it a lot easier for me to digest.”

That’s another way to look at Bubic’s evolution, as a series of smaller parts coalescing -- over the span of several years -- into the dominant pitcher taking the mound every fifth day.

“All those factors put together allow the long-term outlook to look better than it did those first three years,” Bubic said in April.

The same goes for his present, too.