Is Trevor Rosenthal Elite Again?

With the trade deadline rapidly approaching, teams are currently scrambling to put the final touches on their teams. World Series hopefuls seek the player that will get them ‘over the top’ while the less fortunate seek prospects to shape their futures.

One of the names being tossed around is that of Royals closer, Trevor Rosenthal. After immense struggles in 2019, he has been dominating 2020 with an ERA of 1.59 and 11.9 strikeouts per nine innings. How did he go from a double digit ERA to a prime back of the bullpen piece?

PITCH SELECTION

In his time as an elite closer with the Cardinals, Rosenthal was primarily a fastball-changeup pitcher who would occasionally throw a  few breaking balls. Since coming back from Tommy John surgery, the roles of his breaking ball and changeup have switched; he is now a fastball-slider pitcher who mixes in changeups against lefties.

Comparing this year to last, he’s traded a few fastballs for offspeed pitches, but it has not been a substantial change. Certainly not one of the magnitude to explain the shift in performance. If his pitch selection has not changed much, maybe the pitches themselves have.

PITCH SPEED/MOVEMENT

Throughout his career, Rosenthal’s blazing fastball sitting at 98 miles per hour has been his staple. His changeup and slider have sat in the high 80s creating good speed gaps with the fastball they play off of. 

Comparing his three main pitches to their speed-movement profiles last year, there seems to be some notable differences. His changeup gained 2.4 inches of horizontal movement increasing the amount it fades away from lefties. His fastball and slider both gained vertical movement in their respective directions, increasing the gap they form.

These changes help explain his metamorphosis, but not entirely. He was still throwing heat with a biting slider last year. He had elite “stuff” but was just failing to produce in 2019. Even if Rosenthal improved his toolbox going into 2020, there needs to be a significant gain elsewhere to explain his transformation.

PITCH USAGE

Trevor Rosenthal’s main problem in 2019 was a lack of command. He walked over three tenths of the batters he faced. Seeing an inability to throw the ball in the zone, hitters could default to forcing Rosenthal to attack which he was often unable to do. 

In 2020, he countered this lack of aggressiveness by keeping the ball in the zone. Both his fastball and slider have clustered near the middle of the zone, almost daring hitters to swing. Consequently, his Zone% increased, his 1st pitch strike% ballooned, and opposing hitter’s swing rates have neared league average rates. 

By getting ahead and forcing hitters to increase aggression, Rosenthal has also seen his Chase% – the rate at which hitters swing at pitches out of the zone – increase along with his strikeout rate. It was no secret that Rosenthal needed to throw more strikes, but are all these improvements here to stay?

YELLOW FLAGS

If it seemed his pitches were clustering a little too close to the middle of the zone, it is because they are. MLB gameday breaks the strike zone into nine equal boxes with the middle being considered a “meatball”. In 2020, 10.9% of Rosenthal’s locations classify as meatballs. In the statcast era, no pitcher has maintained that rate for 1000+ pitches.

Of those who approached Rosenthal’s meatball rate, most understandably struggled with inducing weak contact. Of the eight seasons in the statcast era where the pitcher threw 1000+ pitches and had a meatball% of 10+, only two were above average in inducing weak contact despite survival bias.

Rosenthal’s xwOBAcon rose from .303 to .361 last night after Miguel Sano and Nelson Cruz hit long overdue extra base hits. That may be a sign of things to come if he keeps attacking the middle of the zone at the rate he does. The strikeout rate is impressive, the walk rate is manageable, but the damage prevention has been unsustainable.

Most ERA predictors now have him sitting between three and four. He may be significantly better than he was last year, but this is not the lockdown closer from the mid-2010s. At his peak, home run prevention was what kept his ERA between two and three. If he wants to return to those levels, he can not just keep throwing the ball down the middle.

A trend to keep an eye on is his Edge%. In his lights-out days with the Cardinals, he sat above league average, but has failed to approach the range since. It is the most advantageous section a pitcher can attack; if Rosenthal wants to return to his truly elite form, he needs to demonstrate the command to out the ball in more favorable locations. If not, the extra base hits will come, dragging him toward mediocrity.