Why Angels' ace stopped throwing his nasty new pitch

Want to be a better big league pitcher? Just add a nasty new pitch. It's that simple.

Except when it's not. That's what Angels left-hander Yusei Kikuchi discovered.

And it turns out, Kikuchi's willingness to not throw his brand-new sweeper is what allowed him to become a second-time All-Star in 2025.

Major League Baseball today is populated by pitchers with expansive repertoires full of trendy pitches -- new splitters, new sinkers, new "kick" changeups, new sweepers.

The "sweeper," just in case you're not familiar, is just a variety of slider thrown slower and with much more horizontal movement than the traditional slider with higher velocity and tighter break. Sweeper usage has exploded around the Majors in the last few seasons, as pitchers have sought out diverse pitch mixes that cover a wide range of speed and movement profiles.

That's what Kikuchi wanted, too.

"I was thinking about how to get some of the tough lefties out," Kikuchi told MLB.com through interpreter Yusuke Oshima. "Guys like Corey Seager, Yordan Alvarez. There's always a way to get them out, and I felt like I potentially needed the sweeper to do it."

Coming into the 2025 season, the Angels' new ace had a fairly traditional repertoire for a starting pitcher: four-seam fastball, slider, curveball, changeup. But because Kikuchi's slider and curveball are more vertical pitches -- they both have downward action, but very little horizontal movement -- that left a hole in his arsenal: Kikuchi didn't have any pitch that breaks away from a left-handed hitter.

Enter the sweeper. It would be the perfect pitch to address that hole in Kikuchi's arsenal and give him the weapon he needed to attack the best lefties he'd face.

Kikuchi developed a sweeper and debuted it in Spring Training. And it looked really good. Kikuchi's new sweeper averaged just over 81 mph with over 15 inches of horizontal break in the spring, while generating a swing-and-miss rate of 33% and a strikeout rate of 40%.

So he took the sweeper with him into the regular season. He threw six of them in his second start on April 2 against the Cardinals, and got a strikeout against Victor Scott II.

But Kikuchi quickly noticed something was awry. Not with the sweeper itself, but with his other pitches. Kikuchi's fastball didn't have its life, and his other breaking pitches, the slider and curve, weren't biting the way they were supposed to. His velocity was down across the board. And his command was off -- Kikuchi walked five batters in that start against St. Louis.

The sweeper was the culprit.

Kikuchi identified the problem. To get the side-to-side movement he wanted out of the sweeper he had to throw it out of a lower arm slot than his other pitches. Which would be fine, if he could isolate that mechanical adjustment to the one pitch that needed it.

But he couldn't. Changing his arm angle for the sweeper was having a ripple effect across his arsenal, and throwing his arm slot out of whack for everything else.

"My slider was becoming a little bit cutter-y, and the curveball wasn't moving as much as it used to," Kikuchi said. "So those two pitches especially, I was looking at that -- and I thought maybe the arm slot was the cause of it."

In 2024, with the Blue Jays and Astros, Kikuchi's arm angle was 42 degrees, per Statcast -- a fairly standard three-quarters release point. But when he introduced the sweeper this year, he was throwing it at a 26-degree arm angle -- much more sidearm. (A lower arm angle is more sidearm; higher is more over-the-top.)

Having to emphasize a lower delivery specifically for the sweeper dragged down Kikuchi's arm slot for everything else he threw. His four-seam fastball arm angle dropped from 39 degrees last season to 32 degrees this April. His slider arm angle dropped from 40 degrees to 31 degrees. His curveball arm angle dropped from 51 degrees to 42 degrees.

For his sweeper, the low arm angle was a good thing. The side-to-side movement for a sweeper can be easier to create from a more sidearm release. But for Kikuchi's four-seamer, slider and curveball, it's bad. He wants the fastball to rise and those breaking balls to drop, and his lower release was counterproductive to that.

"The [sweeper] arm angle messed me up a little bit," Kikuchi said. "There are pitchers who are able to adjust their arm slot very easily, but for me, it was difficult."

That's the thing about pitching mechanics. Every pitcher is different. Not everyone can be a Paul Skenes and pull a "splinker" out of thin air. Some pitchers take years to find their best version of a pitch, like Tarik Skubal and his changeup. What works best for Kikuchi is ... not sweepers. And he can be plenty dominant without them.

Especially at the Major League level, where pitch design has become a complex science and pitches have to be refined to a razor's edge to be effective against the best hitters in the world, changing one thing can have unintended consequences.

For Kikuchi, the negative consequences for his arsenal outweighed the positive impact of having a sweeper for lefty-lefty situations. Three pitches getting worse weren't worth one thing getting better.

So, just as quickly as the sweeper had entered Kikuchi's repertoire, it disappeared.

"If you think about making one adjustment -- like finding a new pitch like a sweeper -- you could probably do that if you keep working on it," Kikuchi said. "But you might forget your other pitches and how you used the throw. So the biggest thing was just eliminating that sweeper."

He hasn't thrown the sweeper since April. And he's been so much better.

Once he stopped throwing the sweeper, Kikuchi began the long process of getting his mechanics back in sync.

He didn't set a goal on raising his arm slot specifically, because he thought focusing too heavily on that would affect the rest of his mechanics, the same way throwing the sweeper did that in the first place. Instead, he made adjustments to the position of his glove hand and emphasized staying back and not flying open during his delivery.

With those adjustments, the arm slot has come along. Kikuchi has managed to raise his arm angle by several degrees since April. Here's what that change looks like for his fastball and slider, his two most important pitches:

And slowly, his stuff has come around, too. Kikuchi's fastball velocity has ticked up from 94.2 mph to 95.2 mph in July. His slider is up from 86.6 mph to 87.7 mph. Those are more in line with where he was in 2024. That's why, by the end of the first half, Kikuchi was at an All-Star level.

The longer he pitches without the sweeper, the closer to the old Kikuchi he gets.

"Not throwing the sweeper, I feel like now I'm able to be like myself," Kikuchi said. "I feel like years past. My velo's there and I haven't been thinking about arm slot."

But Kikuchi still has to get those top left-handed hitters out. And without a sweeper in his arsenal, he's had to find other ways to attack them.

Those strategies have included mixing in more curveballs to lefties to keep them off-balance, running some two-seam fastballs in on their hands so they can't cheat out over the plate and even surprising them with an occasional lefty-lefty changeup, like Kikuchi threw a few times to Shohei Ohtani in their meeting on May 18.

But it's also just about throwing his best pitches with conviction: the four-seamer and slider.

"Eliminating the sweeper, [I've been] sticking to my strengths, and my strengths have always been fastball-slider," Kikuchi said. "So I'll just continue to work on that and believe in those pitches. I think that goes a long way."

There are lessons learned here. Turns out, throwing a new pitch can be easier said than done.

But what about the future? Would Kikuchi consider bringing back the sweeper, for example, after a full offseason of work to make sure it didn't interfere with his mechanics?

Kikuchi didn't need a translation to answer that one.

The Angels ace responded immediately, in English: "No more sweeper."