Luis Severino and Defining the Debut Adrenaline Effect

The first inning of a debut is a sweaty time. Just look at Henry Owens as he stepped to the mound for the first time in the big leagues this past week. Your heart strains for him — not only in sympathy, but also because it’s just so obvious that his blood is racing through his veins and his vision is blurry. You can almost feel it just watching him.


You can see plainly that that the major league debut was full of butterflies for Owens. And so it was for Luis Severino. Just in a different way than most.

We don’t have the debut date for every pitcher in the PITCHf/x era, but we do have 303 pitchers listed. The average debut starter started the game off with 1.3 mph better velocity than he showed in the fifth inning of the same game. That’s a full tick more than the average starter has lost, in-game, this season. So your rookie starter comes out pumping about a tick more than you would expect him to show, based probably on adrenaline.

Later in the rookie season, that same starter will be about three-quarters of a mile per hour below his first inning numbers. That’s despite the fact that velocity peaks in August, and most veteran starters ramp up the velocity slowly as the season goes on. So it does look like rookie starters live on adrenaline for that first start.

Maybe Severino won’t have this problem. He started the first inning average 95… and ended with a fifth inning that saw him average 96 on the fastball. He’s a far cry from Brett Cecil, who started his debut with a first inning average of 94 mph and a fifth-inning average of 86 mph. Severino won’t even go the way of Danny Duffy, who dropped from 95 to 90.7 over the course of his first start.

But that doesn’t mean Severino didn’t have the debut reflux. Take a look at the velocities of his various pitches, thanks to BrooksBaseball. He was tight in the first couple innings — on his changeup and slider. Look how he relaxed and showed better stuff in the latter innings.

Brooksbaseball-Chart (15)

For Severino, it looks like the nerves manifested in his changeup and slider — they were too hard to begin the game. He lost between a tick and two ticks on both pitches between the first and second innings. And in that way, he was conventional — pitchers lost .8 mph on their changeups from the first inning of their debut to the fifth. Tense up, and it seems your changeup tenses up.

By taking something off of those pitches later in the game, Severino gained movement. Between the first three innings and the last two, he gained almost two inches of drop on the slider in particular.

Brooksbaseball-Chart (16)

That’s not typical. Debut starters saw their sliders stay virtually the same between their first innings and fifth innings of their debuts, as well as later in the season — no value was more than .2 inches different, in aggregate.

  1st in Debut 5th in Debut Rookie Season
League FB velo 91.6 90.4 90.9
League CH velo 82.8 82.0 82.3
League SL Zmov 1.4 1.4 1.2

But Severino’s early inning slider looked more like this:


And his later-inning sliders looked more like this:


It’s almost enough of a difference to ask if they were both actually sliders, but contextual clues say they were. Both of these pitches were thrown with two strikes, both were thrown to right-handed hitters (both times Hanley Ramirez), both were six mph slower than his four-seam, and both broke a little to the glove and down. If that’s his cutter and his cutter is six mph slower than his four-seam and breaks so little, it’s a baby slider without the slider break. The second broke a lot more to the glove and down, and looked like a legitimate breaking pitch, either way.

Early in the debut for Luis Severino, he was missing spots. His changeup was too hard, and his slider wasn’t biting. You might have thought he was gas and gas alone. If you turned the game back on in the fourth and fifth, however, you might have seen him hit the outside corner edge of the strike zone on consecutive 3-2 pitches to strike out Mike Napoli. And you might have seen those better sliders and changeups, too.

That’s because every rookie amps it up for the debut. Most do it on the fastball, and Severino did it on the changeup and slider, but it looks like most rookies can’t avoid feeling the effect of the debut jitters.

Bonus leaderboard: the starters that saw the biggest drop from the first inning of their debut and their rest-of-season fastball velocity.

Pitcher First Inning Fifth Inning Season Debut-Season
Brett Cecil 93.6 86.0 89.9 3.7
Wade Miley 92.2 88.2 88.9 3.3
Jeff Locke 91.9 90.5 88.7 3.3
Eddie Butler 95.9 93.5 92.7 3.2
David Purcey 93.9 92.3 91.0 3.0
Mike Wright 95.8 91.9 92.8 2.9
Cody Anderson 95.3 92.8 92.4 2.9
Sean West 93.5 91.1 90.8 2.7
Ethan Martin 95.7 92.6 93.1 2.6
Greg Reynolds 93.0 91.7 90.5 2.4
Drew Hutchison 93.6 91.2 91.3 2.3
Drew Pomeranz 91.8 88.1 89.5 2.3
Antonio Bastardo 93.3 91.2 91.1 2.3
Tyler Matzek 94.4 94.1 92.2 2.2
Jake Arrieta 94.8 93.5 92.6 2.2
Chase Anderson 93.1 91.3 90.9 2.2
Matt Shoemaker 92.9 89.6 90.8 2.1
Brad Lincoln 93.7 91.1 91.6 2.1
Hiram Burgos 89.9 87.4 87.8 2.1
Michael Montgomery 92.9 90.6 90.8 2.1
Tyler Skaggs 91.3 90.4 89.2 2.1

With a phone full of pictures of pitchers' fingers, strange beers, and his two toddler sons, Eno Sarris can be found at the ballpark or a brewery most days. Read him here, writing about the A's or Giants at The Athletic, or about beer at October. Follow him on Twitter @enosarris if you can handle the sandwiches and inanity.

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Mario Mendoza
Mario Mendoza

Maybe the slider difference is not a debut thing: the Yankees commentators stated that they heard he throws two kinds of sliders from folks on the farm. We’ll see if pitchFX bears that out over the next few starts.

Mario Mendoza
Mario Mendoza

Actually that was on the YES postgame show.

Bob Loblaw
Bob Loblaw

He should stop throwing the first one.