Let’s Talk About a Trio of Rookie Starting Pitchers

If you’ve been relying on a rookie starting pitcher, or even multiple, this season to earn you that coveted Yoo-Hoo shower, should you continue to trust them? Will they tire over the final month or suffer increased ratios as the league adapts? Let’s discuss a trio of rookie starting pitchers, how they have performed so far, and how we might expect them to perform the rest of the way.

Paul Skenes | PIT

I was already a fan solely due to the mustache. With a facial hair game like that, it’s automatic top 100 prospect status. Skenes entered the season as the game’s fourth best prospect, sporting an unbelievable assortment of scouting grades. The only pitch of his slapped with a present grade worse than 60 is his changeup, but even that was given a 60 future grade. So that means all four of his non-fastballs have future grades of a 60, to go along with a 70/70 fastball. Oh, and 50/60 command as well.

He shot through the minors after being drafted first overall last year, as he recorded just 34 professional innings before making his MLB debut. Judging by his current results, it’s pretty clear he was ready.

He’s struck out an elite 32.3% of opposing batters, while walking just 5.7%. However, his 12.9% SwStk% and 29.2% CSW% is a bit light for a strikeout rate over 30%. I assumed both of those marks would be higher to support the strikeout rate. The answer for how he’s managed such a high strikeout rate, despite a good, but not great, 29.2% CSW% is the strike type missing from CSW — foul strike rate. He has generated a well above average foul strike rate, and although you can’t record a strikeout on a foul ball, they still help a pitcher get to two strikes, where one more called or swinging strike would end the at-bat. Foul strike rate is the least sticky of the three strike types. That means that unless he starts generating more swinging and/or called strikes, I would expect some strikeout rate regression.

What’s interesting when looking at his pitch type splits is that for one, all of his pitches have generated double digit SwStk% marks. Next, none of his pitches truly stand out as being absolute elite at generating whiffs. The pitch that has generated the highest whiff rate, though, is a shocker — it’s his sinker! Whaaaaaaaaaaaat?! I don’t think I’ve ever seen a sinker generate a 16.3% SwStk% over 400+ pitches. That’s crazy. Even more incredible is that the pitch has generated a 72.7% GB%. So hitters literally either swing and miss or hit it into the ground. That might be the best pitch in the game!

His four-seamer has been excellent with a low double digit SwStk%, but none of his non-fastballs have been very good at generating whiffs, which is surprising. By Stuff+, his slider is his best pitch, and yet it sports the lowest SwStk% among his five pitches. Then again, it has also allowed the lowest wOBA thanks to a .115 BABIP, but I tend to think per-pitch outcomes aren’t really useful in evaluating pitches.

He sports a pretty good batted ball profile, with a ground ball tilt, while also somehow generating a high IFFB%. Usually you see a high IFFB% paired with a high FB%. He has also allowed a low LD%, and whether that’s sustainable or not is anyone’s guess, but the profile is a strong one for both BABIP and keeping runs off the board.

One thing to keep in mind here when projecting his rest of season is that his LOB% stands at an absurd 88.1%. Sure, he’s obviously been really good, but that’s a major reason why his ERA sits at just under 2.00. You can’t possibly project that level to be sustained, so once that rises, and if his strikeout rate falls, he’ll look a bit more ordinary, though still excellent. I’m not sure his perceived value will ever be higher than it is now, so if you’re an owner, he might be a good name to dangle in single-season leagues. In keepers, there’s way more to consider before trading him away of course, but it couldn’t hurt to see what kind of king’s ransom you could get in return.

Hayden Birdsong | SFG

While Birdsong doesn’t have the facial hair game that Skenes brings, he does have an awesome last name. That’s not why he made the latest prospect rankings as the 45th best overall prospect, of course. After looking at Skenes’ scouting grades, it’s hard not to compare the two, and come away unimpressed with Birdsong’s repertoire. Based on the grades, he owns three decent pitches, with a changeup that doesn’t seem like it’s ever worth throwing, and acceptable command. Meh, the grades don’t get me too excited here.

However, the results don’t really match those grades. Birdsong has posted a strikeout rate over 30% at every single minor league stop. You would not expect that given his pitch grades! In the Majors so far over 30.1 innings, nothing has changed. His strikeout rate sits at 30.2%, and it’s actually better supported by his SwStk% and CSW% than Skenes! That’s right, Birdsong has posted higher marks in those two metrics than Skenes, even though I would imagine most or all would argue that Skenes possesses much better stuff.

Birdsong throws hard, though not as hard as Skenes, and has supplemented his fastball with three secondaries. All of them have been fantastic from a SwStk% perspective. In fact, every one of his secondaries sports a higher SwStk% than any of Skenes’ pitches. Of course, it’s only been 30 innings, so it’s possible opposing hitters adapt and Birdsong’s early dominance deteriorates as the scouting report makes its rounds. For now, Birdsong’s repertoire has been elite.

There is one glaring red flag here though — his control. He has posted double digit walk rates nearly everywhere he has pitched and he’s sitting on an 11.9% mark right now. That’s not alarming, but it is pretty high, and near the top of what you’ll ever see a pitch finish the season with who remained in the rotation all year. You essentially need a 30%+ strikeout rate to offset all those free passes, so Birdsong can’t really afford to suffer a whole lot of regression there. Like Skenes, Birdsong has also benefited greatly from an inflated LOB%, which isn’t going to last. His BABIP is also better than average thanks in part to a low 11.6% LD%, which also won’t last.

Overall, you do have to like how he’s thrown three secondaries with high SwStk%, so if one of them isn’t working well in a game, he still has the other two to go to, along with his mid-90s fastball. But is his stuff really this good, given his scouting grades? His SwStk% is higher than it was at Double-A, which you wouldn’t normally expect.

I would worry a bit more about regression here than for Skenes. The control is a problem and I just don’t know if his stuff is really as good as his results have been so far. The projections don’t believe in the strikeouts at all. Though, I’m not sure what’s feeding the models considering he’s never posted a strikeout rate below 30% in his entire professional career, so low-20% forecasts are kinda weird to see.

Spencer Schwellenbach | ATL

Schwellenbach was the least heralded prospect of the trio, though still ranked 70th overall. His scouting grades are mixed, featuring above average fastball and slider grades, a meh curveball, average cutter, and a potentially good splitter, with acceptable command. I have no idea if that mix of grades should produce a high strikeout rate pitcher or not.

As usual, the answer is somewhere in the middle, though Schwellenbach’s strikeout rates have been up and down. It’s interesting that he only posted a 19.6% mark during his debut in Single-A last year, but he’s been at 26% and higher at every level since. What’s also interesting is that he skipped Triple-A and vaulted to the Majors after having pitched just 13 innings at Double-A. So it was a real mystery how he would perform in the Majors after so little upper minors experience.

So far, he has certainly held his own from a results perspective, and those results should perhaps be significantly better. He’s struck out 26.7% of opposing batters and that’s supported by the highest CSW% of the trio, though his SwStk% falls in between Skenes and Birdsong. That CSW% makes me more confident he could maintain that strikeout rate.

He has showcased a six pitch mix(!) that includes a four-seamer that averages just under 96 MPH. He has actually spread out the usage of his pitches amazingly well, as the usage range sits between a low of 9.1% and a high of just 24.6%. I’ve never seen a range that tight! It means that hitters really don’t know what’s coming next.

Four of his six pitches sport a SwStk% in double digits. Wanna hear what his best whiff pitch has been…by far? That “potentially good” splitter that received a 45/60 grade! Guess it has become a 60, or higher, overnight. The pitch sports an absolute elite 27.7% SwStk%, while his next best pitch has been his curveball at 15.6%. The sinker stinks at just 4.5% and has allowed his highest LD% at 40%. If it’s not inducing a massive GB%, it might be time to just ditch the pitch.

In addition to his embarrassing array of pitches, his control has been sterling. His strike rate sits at just over 70%, versus a 64.3% league average, which is amazingly impressive for a rookie. All those strikes have led to a microscopic 3.8% walk rate. So he features a fantastic repertoire and displays pinpoint control?!

It’s clear that Schwellenbach has been mighty impressive, but his ERA is the worst of the bunch at just over 4.00. Yet, both his SIERA and xERA sit at exactly 3.19, so it would seem that he’s deserving of better results. It’s not clear from the luck metrics though as everything looks more or less normal.

Just like any rookie pitcher, and any pitcher with a sub-4% walk rate, the odds are the underlying skills move in the wrong direction. It’s very difficult to maintain such a strong walk rate, and despite his vast arsenal, it’s possible hitters start adjusting and his SwStk% and strikeout rate drop, especially if hitters start laying off that splitter. But so far, so good.