Royals Opening Day rotation hopeful's revamped arsenal looks like the real deal

The Kansas City Royals have a wild number of ties back to the San Diego Padres right now. Whether it be adding former All-Star Elias Diaz on a minor-league deal or the bevy of Royals starters who once wore Padres uniforms, it seems the two franchises are much closer than their geographical distance.

One of those former San Diego-ites (San Diegoans? San Diegans?) is right-handed pitcher Stephen Kolek, who started Saturday's Cactus League game against his former team.

The 28-year-old allowed one run on a solo home run in two innings, striking out two. It was a solid start to his first spring with the Royals after a strong finish to the 2025 season.

Kolek may not break camp in the Royals rotation because the group is deep and full of established options, but big league teams value this kind of starting pitching depth. Kolek is going to have his number called at some point in 2026.

Royals Stephen Kolek's revemaped pitch aresnal look like the real deal

One thing that caught my attention after Kolek joined the Royals last year was how much his arsenal changed. Pitch mix is not static, and Kolek is a good example of how quickly a pitcher can shift gears over the course of a season.

Here is how his usage evolved across 2024, when he was still building a big league starter blueprint.

Each pitch type had ebbs and flows across the season and situation. But this goes to show that an arsenal can greatly change from the season's beginning to the end. Kolek had another round of changes in 2025 with the Padres, making 14 starts from early May through late July. Here is what his mix looked like during that stretch.

When Kolek and teammate Ryan Bergert joined the Royals at the deadline, Kolek carried a respectable 4.18 ERA and 4.42 FIP. He had a dazzling complete game shutout against the Colorado Rockies on May 10, then wobbled later that month and ran a bit inconsistent for San Diego.

Still, he was clearly a competent starter who could help a team down the stretch. Kansas City was still in the postseason picture and needed innings as much as it needed upside.

Kolek delivered. In five starts for the Royals, he posted a 2.00 ERA and ripped off four straight quality starts in September, earning Royals Pitcher of the Month honors.

The results were strong enough that the obvious question followed. What changed besides the uniform and the address? The answer, more than anything, was the process. Specifically, the pitch mix. Here is how his usage looked across those five starts.

It is a small sample, but the trend is obvious. The changeup usage jumped, more than doubling his rate from San Diego. Whatever tweaks the Royals made, they helped him locate the pitch with more intent. PLV graded the changeup as above league average at 5.15 during his time in Kansas City, compared to 4.87 with the Padres.

FanGraphs Stuff+ never really loved Kolek before or after the trade, which is not the point here anyway. The bigger difference was command. Kolek went from below average to well above it after the move. He posted a 98 Location+ with San Diego, then jumped to 108 with Kansas City. That 108 ranked 17th among MLB pitchers from the date of Kolek’s Royals debut onward.

So the question heading into spring training was not whether Kolek could repeat the results. The question was whether the Royals version of Kolek was real. Was this a new baseline, or was it a September tweak that would fade once a new season started?

His first Cactus League outing offered an early hint.

Kolek pitched two innings, allowing three hits with one walk and one run. He struck out two. Here is how his pitch mix looked.

The four seam leading the way is notable, especially with the sinker right behind it. But the bigger takeaway is that the changeup stayed elevated relative to his Padres usage. That is the part that matters most if you are trying to figure out whether the September change was a fling or a foundation.

The overall mix also looks different once you account for platoon splits. Kolek faced 28 left-handed batters and just eight right handed batters in the outing. When you split the usage that way, the plan gets clearer.

Spring results can lie, but usage rarely does. Kolek’s usage screamed continuity. The changeup did not disappear. The four seam was not an accident. And the righty lefty split showed a pitcher who is not just throwing pitches, but throwing plans.

That is why Kolek matters even if he does not break camp in the rotation. Depth starters are not sexy in February, but they win teams games in June. If the Royals keep getting this version of Kolek, the one with real command, a legitimate changeup, and a mix that adapts by matchup, they will have something every contender needs.

Starter quality innings waiting in the wings.