Biggest Starting Pitcher Improvements from April to May

For most of us, April results are not that much more meaningful than the results we get from our teams during the rest of the season. For those of you who play in Cutline leagues, all the power to ‘ya. 

But in practice, April results can have a bit of an outsized impact on fantasy teams. For one, early season-ending injuries are of course more impactful than similar injuries that happen later, since you have more output to backfill. 

And April hot starts can sometimes be parlayed into months of strong performance. That Week 1 streamer who turns into one of the stalwarts of your otherwise lackluster rotation or the top prospect who earned a last minute spot in the starting lineup out of Spring Training. 

We all know these feel good stories. We all know the other side of that coin, too. The early draft pick who limps through April with an inflated ERA. Or who Tatis’s their way through the first nine weeks of the season without a home run. 

In this article, I’ll look at the starting pitchers who have seen the biggest improvements between April and May, keeping things simple by sorting by ERA and K-BB% to trim the fat before getting into meatier analysis on some of the more intriguing arms.

Let’s start with the ERA improvements for those who reached at least 20 innings in both months. 

While I would normally just show the top ten in a given metric to keep things clean, Cristopher Sánchez just tossed a scoreless month, so he deserves a bit of extra recognition. 

Of the above names, only Sánchez and Jacob Misiorowski are anywhere near universally rostered. And like Sánchez, Misiorowski basically went from great to godly in May. 

We’ll focus mostly on the more fringy players. Of this group, did any show underlying improvements that should have us believing, and either holding or buying, in our leagues?

Leave ‘Em Be

Let’s weed out some of the less impressive starters from this group. If you’re not in a 15-team or NL-only league, you were probably already avoiding Miles Mikolas. Who is on the Washington Nationals, in case that’s a surprise for anyone. And who is also running career-worst HR/9 and K/9 rates. Adrian Houser is only slightly more rosterable.

For both Houser and Mikolas, the underlying numbers don’t quite backup the improved ERA. Both starters had their Pitching+ actually decline between April and May, while their xERAs improved by less than a full run, and their K-BB%s improved by 4% or less.

Deeper League Darts

Andrew Abbott, the lone soft-tossing lefty on this list of ERA improvers, actually had no change between his K-BB% in April and May, but both his Stuff+ and Location+ improved. Particularly important for the UVA-product is the improved Location+. As a control artist, when the control goes, the results will likely be shaky at best, and unusable at worst. 

In last season’s breakout, Abbott’s 2.87 ERA was backed up by a 105 Location+. Through April, he was running a 97 Location+, but bumped that up to a 106 mark in May. If he can keep that up, you can keep running him out there in deeper leagues.

But with a greatly diminished strikeout rate thus far, there are certainly risks. Abbott has struck out 15.5% of batters thus far, compared to 21.8% last season. His K% was nearly identical between April and May, so there are no signs of improvement to point to there.

Michael Soroka had suspect underlying numbers as well. While he did shave almost three runs off of his ERA, backed by a two-run improvement in his xERA, his K-BB% was actually 4% worse, falling from 20% through April to 16% in May. His Stuff+ also dropped off a bit, from an already poor 95 down to 92, and his average fastball velocity edged down slightly, from 93.88 mph to 93.39 mph. 

For Soroka, it really is just nice to see him back out on the mound as a full fledged member of a rotation, after finally inching back towards that role with the Nationals and Cubs last season.

With 61 innings under his belt, he’s well on his way to eclipsing his 89.2 from last year, which is certainly a nice surprise for managers and the Diamondbacks alike. Plus, he really does have some nasty stuff.

Just watch out for the home run ball. Thus far, he’s kept his HR/FB down at 6.6%. Last season, that was at 12%, in line with his 13% career mark coming into this season. Home run regression, especially in warm NL West ballparks this summer, could be looming. 

Soroka’s teammate, Ryne Nelson, has had a bit of the opposite problem. Nelson has allowed more home runs than at any point in his career so far, with a 2.07 HR/9 in 2026 compared to a 1.16 mark for his career coming into the season. 

The 28-year-old was a popular flyer for the back half of drafts this offseason, coming off of a 3.39 ERA in 154 innings last season. While April was rough for the young righty, he had a 2.95 ERA in May. His xERA did not really change, dropping just 35 points down to 4.86.

His K-BB% only improved by 2% as well, mainly because of a depressed K%, which is below 20% on the year after getting up to 21.3% last year. Not all is bad though, as his Location+ jumped from 99 through April to 105 in May. Let’s see if he can at least limit the damage of home runs by keeping the walks down and upping the punchouts this summer.

And last amongst the less exciting starters from this group, is Zack Littell. The veteran hurler has also been a victim of the long ball, serving up a 2.28 HR/9 this season, compared to a 1.46 career mark heading into this season.

This seems to be a blip though. And not just because Bo Bichette somehow caught him for a bomb. 

After allowing two or more home runs in five of his first six starts this season, he has settled in with a 0.59 HR/9 in May, allowing just two home runs in six May starts. This helped him improve his ERA by 5.5 runs, backed up by a four-run drop in xERA. His K-BB% and Pitching+ improved slightly as well. He’s just fine. And if no one in your 12-teamer has picked him up during his solid May, go ahead and do so yourself.  

This Could Be Real? (Especially for Roki)

Now for the fun ones. From that earlier list, here are the four names who have improved their K-BB% by 10 points or more, cut their ERA by three runs or more, have had this backed up by shaving at least a run off their xERA, and saw five-point improvements in Pitching+.

Bryan Bello has been a completely different pitcher when pitching with an opener. When Michael Baumann discussed Bello’s early struggles back on May 19, he outlined how Bello had actually pitched well behind an opener during his first two May appearances. The third May start, without an opener, was where he got hit around in Atlanta. And his final two May appearances saw him strike out 10 over 12 shutout innings. 

Even last season, when his 3.35 ERA was backed up by an unconvincing 4.48 xERA and 6.70 K/9, was never as bad as his April was this season. And given all the turmoil surrounding the Red Sox again this season, managers should more or less give him a pass. If you want to use him in leagues shallower than 15 teams, just pay attention to if he’s got an opener, at least for now. 

Anthony Kay is back in the majors after two seasons in the NPB with the Yokohama DeNA BayStars. He put up a 1.74 ERA in Japan last season, though he struck out less than a batter per inning. With the White Sox this season, the 31-year-old lefty has a K/9 of just 6.59. But, especially in May, he started doing some things we should at least take notice of.

For one, he seems to be fully stretched out, going five or more innings in each of his six May starts after doing so just once in six April appearances. This helped him win four games for the rolling South Siders. He also cut his walks dramatically, from a 5.04 BB/9 through April down to 2.87 in May. This accounts for most of his improved K-BB% and explains how his ERA and xERA each fell by about four runs. 

Rostered in 33% of CBS leagues and 19% of Yahoo leagues, he faces the Phillies on the road this week. So it’s probably safe to leave him on your wire. Adding him to your watch list wouldn’t hurt though. 

And while the Mizard is the most awe inspiring member of the pared down list, his acehood has been well-covered, most recently by Jay Jaffe. 

So we’ll focus on Roki Sasaki to wrap things up. 

No one seems to believe in him, except for the Dodgers. And that’s really the signal we all should have been paying the most attention to. With River Ryan carving up AAA, the April struggles from Sasaki could have meant a demotion. After all, the team sent him down last season amidst a tough rookie season. 

This year though, the team stood pat through a 6.35 ERA through April. The Dodgers, and any enterprising fantasy managers, were rewarded by an 18-point jump in Pitching+, which mostly is thanks to greatly improved locations. Mike Podhorzer noticed the improved Pitching+ for Sasaki a few weeks back, and a week later Justin Mason cautioned a wait and see approach, especially with a start against the Phillies coming up. The second-year starter struck out 7 over 5.1 innings against the Fightins, allowing just one run and walking one. 

In May, the results weren’t the only change for Sasaki. He changed his pitch mix. Specifically, he split up his offspeed pitches into a distinct splitter and forkball. David Adler noted this for MLB.com back on May 17, citing Lance Brodzowski, who noted the change back on April 26, crediting the reporting of Katie Woo. As noted by Adler, Statcast changed how they classified Sasaki’s pitches, registering the slower pitch as a forkball, and the new faster version as a splitter. 

According to Fangraphs game logs, Sasaki didn’t even throw a forkball or splitter in a start this season until April 25 against the Cubs, though this seems to be more of a pitch classification issue. That is telling in of itself, since his slider and forkball seem to be the two that blended together.

Savant classified the forkball and splitter as distinct pitches beginning on May 11 in an outing against the Giants. If you just separate his season using these dates as cutoff points, the story really begins to unfold. 

Clearly, he’s a better pitcher when he has more than just the fastball and slider in his arsenal. And having enough control to manipulate his off speed offering and turn it into two distinct offerings will only make it harder for hitters to square him up, especially as he continues to tinker and adjust to the majors.

The Fangraphs Lab Paired Pitch tool does a good job demonstrating the gap between these two now-distinct pitches.

On the left is Sasaki’s pitch mix through his April 19 start, the last before he began throwing a distinct splitter (darker teal on the right) and a distinct forkball (the lighter teal), which are shown on the graphic on the right, depicting his mix from his April 24 start on.

The Fangraphs Lab Paired Pitch tool shows the relative pitch characteristics. Playing off a fastball at the top of the zone, you can see how the splitter adds a pitch with less drop than the slider and forkball. The tool also provides readouts on some of the pitch metrics. Below are the two readouts for the same two periods charted above, Sasaki’s mix before and after adding a distinct splitter.

There some changes to the drop and IVB on the fastball, which could be worth further exploration. But the biggest change is how the splitter slots into his arsenal at a different velocity, 7 mph less than the fastball and 4 mph faster than the slider or forkball. Plus, there’s 6 inches less drop on the splitter than there is on the forkball. If blending pitches together is considered to problematic for a pitcher’s arsenal, Sasaki and the Dodgers clearly have found a way to help separate his offerings to keep hitters guessing.

Remember, he’s only 24 years old, there’s still room to grow. 

Sasaki is already rostered in 71% of CBS leagues, but is on only 45% of teams on Yahoo. If he’s available in your league, and especially if you need a shot at some wins and strikeouts, run, do not walk, to add the young flamethrower. He’s lined up for a rematch against the lowly, and strikeout-prone Angels, who he already carved up in May (8 strikeouts in 7 one-run innings) on Friday this week. After that, he’s likely to face the Pirates or White Sox on the road before taking on the Rays or Orioles at home. June could be just as kind to the youngster as May was.