Reviewing the Rookie Starting Pitchers — Through May 9, 2023

Yesterday, I reviewed the five rookie starting pitchers who have posted a sub-4.00 SIERA so far. Now let’s discuss some of the other well-regarded prospects who haven’t been as fortunate, posting weaker skills.

Hunter Brown was only expected to hold a rotation spot until Lance McCullers Jr. returned from the IL. Now with two more members of the Astros rotation on the IL, one of whom isn’t going to return this season, it’s likely that Brown remains in the rotation for the rest of the season. I loved his skill set heading into the season, as he showcased both strikeout ability and an extreme ground ball rate. His skills have weakened this year, but are still intriguing and certainly good enough to be startable in the majority of league formats and sizes.

He has thrown his slider significantly more often this year at the expense of his four-seamer, which typically results in a higher strikeout rate. However, his strikeout rate has actually declined, though his SwStk% has remained identical. It was to be expected that he would suffer a decline in strikeout rate given the full-time move to the rotation, but his SwStk% is underwhelming. All three of his primary pitches have recorded below league average SwStk% marks, even while averaging 96 MPH with his fastball and peaking at 99. Given his pitch grades, I expected a far greater ability to miss bats, though he wasn’t exactly a great bat misser in the minors either.

I would be fine holding onto him and hoping he could translate his stuff into swings and misses, but his ERA is likely to rise as both his SIERA and xERA are far above his actual ERA, thanks to a tiny 4.2% HR/FB rate that isn’t going to stay that low.

Tanner Bibee was ranked as the Guardians’ fourth best prospect heading into the season and surged through the minors, making it from High-A to Triple-A in essentially one season and a couple of weeks. His strong strikeout and whiff rates haven’t yet translated to the Majors, as his SwStk% is actually just below double digits. Despite averaging 95 MPH with his four-seamer, it has been poor at inducing whiffs, with just a 4.3% SwStk%. His slider, rated as his best pitch, is essentially average for the pitch type, while his curveball has been weak, and his least used changeup has actually generated his highest SwStk%. Strikeouts are a concern given that he’s been an extreme fly ball pitcher throughout his career, so the more balls in play, the more home runs he’s likely to allow. Luckily, he’s posted just a 5.3% HR/FB rate, so home runs haven’t been a concern, but they could be once that rate moves toward league average. He seems in that streamable/pick your starts tier in shallow (12-team) mixed leagues right now.

It looks like Mason Miller has dodged a bullet, at least for now, and should return at some point in the near future. Injuries have limited him to very few professional innings, so it’s very difficult to guess at his true talent. All I see right now is a pretty good strikeout rate, but a mediocre SwStk% and weak CSW%, suggesting he won’t sustain that strikeout rate unless he starts inducing more whiffs and/or getting more called strikes. He’s yet another with a big fastball at 98.7 MPH who for whatever reason, just hasn’t translated it into swings and misses. Its 7.6% SwStk% is meh, but his other three pitches are at least all in double digits. He’s been an extreme fly ball pitcher, even more so than Bibee, with a FB% in the mid-50% range. Like the others, home runs haven’t been a problem because he’s posted a microscopic 3.4% HR/FB rate. He’s in the right home park to be a fly ball pitcher, but no one’s true talent is that good. He seems like a real crapshoot, between his current elbow issue, lack of performance, and stuff not generating a whole lot of swinging or called strikes so far, while allowing tons of fly balls.

Speaking of lower SwStk% marks than expected, Hayden Wesneski ain’t fooling anyone this year. Interestingly, his four-seam velocity is actually up this year, but this highest SwStk% recorded by any of his pitches is just 11.1% from his cutter. His slider is at just 10.3%, while the rest of this expansive five-pitch mix is in the mid-single digits. Every single pitch is worse than during his 2022 debut. With a 4.81 SIERA and 5.81 xERA, and only a mid-teen strikeout rate, he’s unstartable in any league format in my mind.

It’s been a bizarre debut for Kodai Senga, who signed with the Mets after a career in Japan. His stuff seems good, featuring a four-seamer that has averaged 96.4 MPH, and three other pitches ranging from 82.4 MPH to 90.7 MPH. But everything aside from an elite splitter has struggled to generate swings and misses. His splitter sits at a 22.4% SwStk%, which is fantastic, but the rest are in single digits. What’s weird is the high CStr%, as you think of his repertoire as mainly inducing swings and misses, not dropping in there for a called strike. I like the high GB%, but obviously the elephant in the room has been his control, or lack thereof. With a 15.6% walk rate, he’s been walking on a tightrope and has really lucked out to post a 3.38 ERA. That’s thanks to a low .256 BABIP and clearly unsustainable 87.5% LOB%. Luckily, control is seemingly easiest to improve upon, so I am cautiously optimistic about his future, but only if he can get his walk rate into single digits.