Are You For Real? Surprising Fantasy Baseball Pitcher Starts From Jose Soriano and Yilber Diaz

7 months ago by Elliott Baas

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2. Yilber Diaz, Arizona Diamondbacks, 13% Rostered

Welcome back to the "Are You For Real?" series as we dive into Week 17 of the 2024 fantasy baseball season. This week, we've got two young right-handers who pitch out west. First, we'll break down a superb start from Jose Soriano of the Angels. Then, we'll deep dive into Yilber Diaz's exceptional debut week in Arizona.

For those who are not familiar, this is a weekly column where we take starting pitchers who had surprisingly good starts over the past week and put them under the microscope to determine whether they're legit or just smoke and mirrors.

Roster percentages are taken from Yahoo! and are accurate as of July 15.

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Jose Soriano, Los Angeles Angels, 16% Rostered

2024 Stats (prior to this start): 81.1 IP, 3.87 ERA, 4.09 FIP, 11.1 K-BB%
7/13 vs. SEA: 6 IP, 5 H, 1 ER, 4 BB, 5 K

Soriano was effective on Saturday, allowing just one run over six innings against the Mariners. He earned his fifth victory of the season and lowered his ERA to 3.71 in the process. This was his best start since returning from the injured list, where he spent three weeks due to an abdominal injury. Soriano has had some flashes of effectiveness at times this season, and has been allowed to pitch deeper and deeper into games by Los Angeles. Is he worth adding for the long haul, or should he be left on waivers?

Originally an international free-agent signing by the Angels, Soriano was not a highly regarded prospect. He signed for just $70,000 and was left unprotected by the Angels and subject to the Rule 5 draft in 2021, where he was selected and subsequently returned to the Angels by the Pittsburgh Pirates. Soriano works with a five-pitch mix consisting of a sinker, knuckle curve, four-seam fastball, splitter, and slider.

Soriano may throw a lot of different pitches, but make no mistake, his bread and butter has been the sinker. A hard 97.8 mph offering, Soriano uses this pitch 42.1% of the time, making it by far his most-used pitch. He exceeded that usage rate in this start, throwing the pitch 54% of the time against the Mariners. In addition to its exceptional velocity, Soriano has exceptional movement with his sinker, with the pitch dropping 24% more than the average sinker. Here’s an example from this start.

Jose Soriano's sinker pic.twitter.com/oCOJ90vWtz

— Elliott Baas (@ElliottBaasBB) July 16, 2024

It's not hard to make Jorge Polanco miss, but that’s still an impressive offering, and Soriano earned seven of his 16 whiffs with his sinker in this start. Those seven whiffs were nice to see, but strikeouts aren’t what one should expect from Soriano’s sinker. He has just a 6.7% swinging strike rate and 26.2% chase rate with the pitch this season. The sinker does do one thing extremely well, and that’s induce ground balls. Soriano has a wild -7-degree average launch angle against the pitch, along with a 72.9% ground-ball rate. Soriano also has a 60.2% ground-ball rate overall, which is second highest in the majors among starters (min. 80 IP). This writer is a fan of pitchers who possess extreme skills in one area or another, and Soriano certainly fits the bill as a ground-ball specialist.

So, the ground-ball prowess is great to see, but what else does Soriano have to offer? His next most-used pitch is his knuckle curve, which he throws 26.5% of the time. Opponents have struggled with this pitch thus far, batting just .205 off the curveball with a .397 SLG and .300 wOBA. The expected stats are somehow even better, with Soriano sporting a .181 xBA, .354 xSLG, and .273 xwOBA with his curveball this season. He also has a 15.2% swinging strike rate and 32.6% chase rate with the pitch this season, making it one of his best strikeout options. With 2,439 RPM and 5.7 extra inches of break compared to the league average curveball, Soriano’s curve looks like a solid secondary offering and the perfect complement to his sinker.

While these two pitches represent a strong foundation for Soriano, he’s also gotten excellent results with his splitter. He throws the splitter almost exclusively to lefties, and opponents are hitting just .143 against the pitch with a .314 SLG and .181 wOBA. The expected stats suggest the pitch has overperformed thus far with a .237 xBA, .418 xSLG, and .302 xwOBA. Soriano has just a .167 BABIP against this pitch, so it’s easy to envision that number rising over time for him. Still, the pitch has plus break and drop and a 16.8% swinging strike rate, so it’s another solid offering at Soriano’s disposal. He’s fared much better against lefties compared to righties this season (.244 wOBA vs. L, .363 vs. R) and the splitter is a big reason how he’s done it.

Soriano has a solid repertoire to support his 3.71 ERA, but there are still flaws to be concerned about here. First, Soriano has had problems throwing strikes at times. He issued four walks in this game and has just one start all season where he hasn’t issued a walk. He’s issued multiple walks in nine of his 15 starts thus far. Control has long been an issue for Soriano, and his current 9.4% walk rate is actually a big improvement over 2023, when he had a 15.4% walk rate at Double-A and a 12.4% walk rate in the majors. Still, Soriano is issuing his fair share of free passes, which could lead to a higher WHIP and more runs against him, especially if his .264 BABIP against rises. His extreme ground-ball tendencies could keep his BABIP relatively low over the course of a full season, but I’d still expect regression on his current BABIP.

Second, Soriano’s four-seam fastball has been clobbered this season. Batters are hitting .333 against the pitch with a .590 SLG and .434 wOBA. The expected stats suggest that Soriano has been unlucky with this pitch as he has a .255 xBA, .482 xSLG, and .362 xwOBA off his four-seamer. Those expected stats paint a rosier picture sure, but Soriano is also allowing a 92.9 mph average exit velocity and a 19-degree average launch angle against his four-seam fastball.

Home runs aren’t a big issue for Soriano overall thanks to his ground-ball prowess; however, he could surrender his fair share off the four-seamer given these batted ball numbers. A major league pitcher can get away with walks or home runs, but not both. He’s begun throwing his four-seamer less often, using it just 9.2% of the time in this start (16.5% season usage), which is a good thing since Soriano’s four-seamer could be a liability for him on the mound.

Verdict:

Soriano does one thing extremely well, and that’s induce ground balls. That alone makes him interesting from a fantasy perspective, but throw in two effective secondary pitches in his knuckle curve and splitter, and you’ve got an exciting young arm. He issues too many walks and his four-seamer has been a liability, but ultimately there is more bad than good in this profile.

Furthermore, at just 25 years old and new to starting pitching (he worked out of the bullpen prior to 2024), Soriano has plenty of room and potential for growth down the line. He could be a poor man’s Framber Valdez since he induces so many ground balls but allows his share of hard contact. He might carry a high WHIP thanks to his control issues, so he should be avoided if one is trying to protect or improve that category. But if you have a little wiggle room at WHIP, I think Soriano is worth a flier in 12-team leagues or deeper as a solid streamer or back-end starter.

Yilber Diaz, Arizona Diamondbacks, 13% Rostered

2024 Stats (AAA): 22 IP, 3.27 ERA, 3.78 FIP, 20.9% K-BB%
7/8 vs. ATL: 6 IP, 4 H, 1 ER, 1 BB, 5 K
7/13 vs. TOR: 6 IP, 4 H, 1 ER, 2 BB, 2 K

Diaz had quite the debut week for the Diamondbacks. First, he held the Braves to one run on four hits over six innings in his first career start, and he followed it up with a nearly identical line against the Blue Jays in his second career start. Diaz is riding high into the break at 1-0 with a 1.50 ERA. With expected rotation pieces such as Merrill Kelly, Eduardo Rodriguez, and Jordan Montgomery all on the shelf, Diaz has the perfect opportunity to seize a regular rotation spot in Arizona. Is the young right-hander a fantasy asset, or an arm to ignore?

Originally an international free-agent signing in 2021 out of Venezuela, Diaz rose from obscurity to become a highly ranked prospect in the Diamondbacks system. He ranked as Arizona’s No. 6 prospect by FanGraphs in May 2024 prior to his promotion. An undersized right-hander at 6-foot-0, 190 pounds, Diaz works with a three-pitch mix consisting of a four-seam fastball, slider, and knuckle curve.

He may have three pitches to choose from, but Diaz leaned heavily on his fastball in his first two starts. He’s thrown the pitch a combined 60.6% of the time. The pitch has performed well for him, with opponents batting just .226 with a .387 SLG and .290 wOBA against Diaz’s fastball thus far. A 96.1 mph offering, Diaz boasts both plus velocity and plus horizontal movement with his fastball. His fastball was considered his best pitch by scouts, and he’s gotten exceptional results thus far.

Whether he can sustain these results is another story. The batting average against might be low, but batters have pulverized his fastball for a 93.1 mph average exit velocity and a 28.6% line drive rate. He’s been rather fortunate to have .222 BABIP against his fastball with these batted ball numbers, but it’s a small enough sample size that wonky outcomes like this aren’t unheard of. The expected stats of a .285 xBA, .387 xSLG, and .342 xwOBA probably paint a more realistic picture of what to expect from Diaz going forward.

His next most-used pitch has been the slider, which has also been excellent for him. In fact, he has yet to surrender a hit against the pitch and has a 69.8 mph average exit velocity against. The pitch is characterized by its exceptional spin and horizontal break. Diaz has averaged 2,706 RPM with the pitch thus far, which is quite high for a slider. He also has 8.5 additional inches of break with the pitch compared to league average.

He has routinely thrown it down and away from hitters through two starts and it was especially effective for him against the Blue Jays, where he earned five whiffs on eight swings with it. Diaz may only have a 15.6% strikeout rate through his first two starts, but with his plus velocity and high movement slider, there’s the potential for a better strikeout rate down the line. He was above 30% at Triple-A and Double-A this season prior to his promotion. Don’t expect a 30%+ strikeout rate in the majors, but he could certainly do better than his current 5.25 K/9.

Diaz rounds out his repertoire with a knuckle curve, a pitch he’s thrown just 9.4% of the time thus far. He only threw nine knuckle curves against the Blue Jays and failed to earn a whiff with the pitch. Given the relatively low usage rate, Diaz is almost a two-pitch pitcher. The knuckle curve seems to be his secondary option against lefties and a show-me pitch against righties. Perhaps he will expand his usage over time, but for now, don’t expect too much out of Diaz’s knuckle curve unless he’s facing a lefty-heavy lineup, in which case he might struggle as he won’t be able to rely on his slider as much. Thus far, lefties have a .320 wOBA against Diaz, compared to a .217 wOBA for righties.

Between the fastball and slider, Diaz has solid stuff, but let’s make one thing clear: He’s been incredibly lucky through his first two starts. He has a .206 BABIP against and a 93.8% LOB rate, both of which should severely regress toward league average. When that happens, his ERA and WHIP should rise closer to the 3.83 FIP or even the 4.35 xFIP he’s posted. Diaz has also struggled with control as a minor leaguer. He had a 9.9% walk rate at Triple-A and a 12.9% walk rate at Double-A this season. He’s only issued three walks thus far, but I would expect walks to be a problem for him until he shows us otherwise over a longer period of time.

Verdict:

Diaz is a raw talent, but his fastball and slider both look like solid offerings. He has plus fastball velocity and above-average spin and movement with his slider. His third pitch, a knuckle curve, leaves something to be desired, but it does round out his repertoire. He’s thrown the fastball or slider more than 90% of the time thus far, so Diaz is almost a two-pitch pitcher. He has struggled with control as a minor leaguer and I don’t trust his 6.7% walk rate to hold over the course of the season. He’s also been incredibly lucky thus far and his 4.83 SIERA should give any fantasy manager pause before throwing him in the lineup.

Still, Diaz is widely available and this might be the only chance to get him in deeper leagues. He’s worth a stab in deeper leagues if you need a starter and can weather potential volatility. It’s too early to trust him in 10- or 12-team mixed leagues unless one is really desperate for an arm, though I’d prioritize Jose Soriano over Diaz if both were available.

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