3 Impressive Fantasy Baseball Breakout Pitchers - Who's For Real, Who's Not?

April 23, 2025

Kevin analyzes 3 starting pitcher fantasy baseball breakouts, sleepers who are off to hot starts in 2025. Who is for real, and who is due for regression?

As we head into late April, we can start to gain a better understanding of who's in for a solid season and who may need to dig themselves out of the trenches. Today we'll focus on three surprising pitchers who are off to hot starts this season.

We'll dissect their numbers, examine their usage of their arsenal, and try to determine whether they're due for positive or negative regression, or if their approach can be consistent throughout the rest of the season.

Identifying positive or negative regression can give you a huge leg up in your league. So let's jump into things and head down to Tampa for our first pitcher evaluation.

Drew Rasmussen, Tampa Bay Rays

2025 Stats: 0.87 ERA, 28.9 percent K%, 1.63 FIP, 2.81 xFIP

It's a bit easy to forget just how dominant Rasmussen has been since he arrived in Tampa, but a lengthy absence due to injury can do that. His start to 2025 serves as a reminder that he can be the ace of a staff when healthy.

The right-hander has amassed a minuscule 0.87 ERA in his four starts this season. He hasn't allowed multiple earned runs in any game. That includes a one-run performance against the New York Yankees, the league's most productive offense.

Filth from Drew Rasmussen to start the game pic.twitter.com/qo1yZ61XfX

— Jake (@TBRaysCentral) April 18, 2025

Much of this is being driven by a change in his pitch mix. The usage of his cutter and four-seamer has essentially swapped from year to year, with an increase in his cutter (27.7 to 34.2 percent) and a decrease in his four-seamer (37.7 to 29.7 percent).

Those two pitches dominate his pitch mix, both holding an xwOBA of .220 or lower. He's also throwing a sinker and a sweeper, but both hold an xwOBA above .400, and he's rightfully not prioritizing those pitches.

When looking at his batted ball profile, we can see that he's getting fewer groundballs this season and is seeing an increase in flyballs. Hitters haven't been capitalizing on those flyballs, though, as they're averaging an 11.5 degree launch angle off Rasmussen, and that's turning into weak outs.

Given the 29-year-old's stats from the past few seasons, we can see that he's incredibly consistent from year to year. He's had four straight seasons with an ERA at 2.84 or below, which should give us more confidence that even with some potential negative regression, he'll continue to excel.

You simple aren’t going to find many more dominant sequences than this from Drew Rasmussen pic.twitter.com/0gK6YRTW97

— Jake (@TBRaysCentral) April 12, 2025

All that's to say that Rasmussen's season is for real. His 28.9 percent strikeout percentage will rack up the fantasy points for you, and he'll keep finding ways to limit hitters as much as possible. Buy in on Rasmussen.

Casey Mize, Detroit Tigers

2025 Stats: 2.22 ERA, 18.9 percent K%, 4.02 FIP, 4.43 xFIP

Might it surprise you to know that it's Casey Mize, not Tarik Skubal, with the best ERA of Detroit's starters? The 27-year-old is making his mark early this season for the Tigers as they fight to prove their late-season run in 2024 was no fluke.

While Rasmussen's start looked to continue the trend building in his career, Mize's start looks to be a bit of a shock. In 2024, he posted a 4.49 ERA, something we'd expect with his 4.20 career ERA. So a 2.22 ERA feels like a bit of an overachievement.

When factoring in his 4.02 FIP and 4.43 xFIP, it certainly appears that Mize is overachieving and that negative regression is on the horizon for the righty. What's driving that is a low strikeout percentage (18.9 percent) that doesn't quite help balance out an average walk percentage (7.4 percent).

At the same time, Mize's .250 wOBA is fairly balanced out to his .249 xwOBA. That means he's getting soft contact despite the additional balls in play, exemplified by his career-best 34.3 percent hard hit percentage.

His batted ball profile is reminiscent of what we saw with Rasmussen as well, with a decrease in groundballs and an increase in flyballs. However, the variance on each from season to season (49.0  to 38.6 percent for grounders, 29.6 to 48.6 percent for flyballs) is much more drastic.

"Wait until Casey Mize pitches against a real team!"

Ok, against the Yankees:
6IP | 4H | 1R | 3BB | 6K | 88 Pitches

Convinced yet? MIZE IS HERE! pic.twitter.com/mCfaE6l1sk

— Joe M (@jFudgy_) April 7, 2025

Mize gets the benefit of pitching in Comerica Park, easing some of the worries about an increase in flyballs. However, it does mean that eventually those flyballs are going to turn into home runs more often than we would like to see.

Another aspect of negative regression that's not all that promising is the difference in his four-seamer's wOBA (.237) and xwOBA (.365). With his four-seamer being his most-used pitch at 34.6 percent, it's not quite what we want to see.

That does get balanced out with expected improvement from his split finger (.201 wOBA, .126 xwOBA) and his slurve (.354 wOBA, .206 xwOBA). It makes for a bit of a tricky case for Mize in terms of how to project the rest of his season to go.

Casey Mize, Vicious 86mph Splitter. 😤

6th K pic.twitter.com/aZf66SpMHZ

— Rob Friedman (@PitchingNinja) April 7, 2025

As of now, it's hard for me to say that we can expect Mize to continue his hot start throughout the season, and negative regression is coming for him through the lack of strikeouts and increased flyballs he's getting. However, it shouldn't hit him as hard as his FIP and xFIP suggest it may.

Tyler Mahle, Texas Rangers

2025 Stats: 0.68 ERA, 24.8 percent K%, 2.51 FIP, 3.80 xFIP

Maybe the biggest surprise on the mound so far this season is what Mahle has done with the Rangers, allowing only two earned runs in just over 26 innings pitched. After missing the majority of the past two seasons due to Tommy John surgery, it's precisely what Mahle and the Rangers wanted to see.

Mahle's biggest strength this season is that hitters just aren't getting to him. His .185 wOBA ranks as best in the majors, while his xwOBA of .275 ranks 15th, still a great place to be and sandwiched between Logan Webb and Garrett Crochet.

Tyler Mahle, Elevated 95mph ⛽️ pic.twitter.com/QcCScUVmNd

— Rob Friedman (@PitchingNinja) April 20, 2025

For the most part, his pitch mix hasn't changed much from year to year. He's dominant with his four-seamer, throwing it more than half the time, while his split finger, slider, and cutter round out his arsenal.

All of his pitch mix currently has negative regression coming with the most impactful regression likely to be with his split finger (.198 wOBA and .300 xwOBA). His four-seamer will have a similar increase, making his top two pitches vulnerable to more damage.

ok tyler mahle pic.twitter.com/ajSNu345FB

— kennedi landry (@kennlandry) April 9, 2025

When looking at his batted ball profile, not much has changed at all from season to season. The most noticeable difference is that he hasn't given up a HR yet after having just a 6.7 percent HR/FB ratio in 2024, much lower than his career mark of 13.9 percent.

The biggest worry with Mahle right now comes from his walk rate, currently sitting at 11.9%. If he can't gain a bit more control of his pitches, then negative regression is going to hit him even worse when hitters start making more solid contact with more runners on.

Overall, we should expect Mahle to regress to a mark similar to his 2021 season with the Reds, where his 3.74 xFIP matches up well with his current 3.80 xFIP. He's not going to be a dominant ace as we advance, as he's benefited from luck, but he'll be a very serviceable piece in both the Rangers' rotation and fantasy lineups.

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