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Revisiting the possibility of Trevor Rosenthal as a starting pitcher

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Michael Wacha is the obvious replacement for the Tommy John-bound Alex Reyes, but Trevor Rosenthal has long been interested in getting his shot in the starting rotation.

Milwaukee Brewers v St Louis Cardinals Photo by Scott Kane/Getty Images

Though seemingly inevitable these days, it is still never fun to lose a pitching prospect, especially one as highly regarded as Alex Reyes. And while this may sound naive and somewhat contradictory considering the heaping amount of praise I’ve given Reyes this offseason (starting at the 29:00 mark), the St. Louis Cardinals will probably be fine in 2017, unless, of course, another significant pitching injury materializes.

Fortunately, once again due to the depth created and preserved under the watchful eye of general manager John Mozeliak, the Cardinals have a handful of options to replace Reyes’ spot in the rotation, with some being more exciting than others. The “boring” choice, in my opinion at least, would be Michael Wacha, who lost his arbitration hearing yesterday, subsequently setting his 2017 salary at $2.775 million (versus the $3.2 million he had requested). An up-and-coming choice would be Luke Weaver, as our own John Fleming discussed yesterday. The newly-acquired John Gant could be an option as well. Today, I argue, just as I did way back on January 24th, 2014, the case for Trevor Rosenthal, starting pitcher.

Now, I fully understand that Rosenthal has not started a single game since his time with the Springfield Cardinals and Memphis Redbirds in 2012 (for reference, that year, prior to his MLB promotion, Rosenthal averaged 86 pitches per start). Four and a half years removed from starting is a very long time. Since joining the big league club at the tail end of 2012, Rosenthal has averaged essentially one inning per appearance — 277.1 innings over 278 appearances. Thus, I cannot even begin to predict how Rosenthal would be able to handle a full starter’s workload.

What I can say, though, with absolute certainty, is Rosenthal has trained all offseason to be a starting pitcher. As we have learned over the years, the idea of moving back into the starting rotation has long been on Rosenthal’s mind, even during his time as an “elite” closer. In November, Derrick Goold reported that Rosenthal was to be “stretched out for a different role,” which we had since learned was more likely to resemble that of Andrew Miller than that of a starting pitcher. However, that interpretation came before the news broke that Reyes would be sidelined for the entire season — a role-altering development.

Other than the fact that he used to be a starter, is there even a foundation present for Rosenthal to be successful as a starting pitcher? After all, Kevin Siegrist also used to be a starting pitcher (back in 2012 as well, with Palm Beach, Springfield, and the Fall League), and I don’t see anyone clamoring for him to get his shot in the rotation (heck, he might even be hurt now, too). To answer the question, yes, there is a foundation for Rosenthal to be a starting pitcher. The foundation is bolstered by a capable and still-adapting repertoire, allowing him to be effective against both righties (.310 wOBA) and lefties (.263 wOBA) and for multiple times through a batting order. Here’s a look at his repertoire, via BrooksBaseball.net:

Remember, regarding horizontal movement in right-handed pitchers, a negative value means arm-side movement, whereas a positive value means glove-side movement.

Trevor Rosenthal Repertoire

Pitch Type Frequency Velocity (MPH) Horizontal Mov. (in.) Whiffs/Swing GB/BIP
Pitch Type Frequency Velocity (MPH) Horizontal Mov. (in.) Whiffs/Swing GB/BIP
Fourseamer 77.78% 98.13 -3.18 27.18% 43.90%
Changeup 14.08% 88.13 -6.57 38.07% 52.71%
Slider 3.58% 87.98 3.29 29.41% 54.84%
Curveball 4.23% 81.27 5.09 18.31% 54.84%

A big portion of what made Reyes exciting as a starting pitcher — the high-powered fourseamer followed by the threat of a devastating changeup — Rosenthal already possesses, in almost certainly a more polished manner. And yes, I make the “more polished manner” statement under the assumption that Rosenthal’s crazy walk rate last season was a fluke — an executive decision I am choosing to make. Let’s take a look:

The fourseamer (BrooksBaseball At Bat)

Of note, Rosenthal threw Kris Bryant — one of the league’s very best hitters — five straight fourseamers in this at bat, and he was still able to record the strikeout (with some help from Yadier Molina’s framing and the home plate umpire’s strike zone). Being able to move the pitch in and out, up and down makes it seem like he is being more complex than throwing the same pitch over and over again — and we can just ask Lance Lynn how this approach works.

The changeup (BrooksBaseball At Bat)

After five straight fourseamers (maintaining an average velocity of 100.1 MPH), Rosenthal pulled the string on a 90.4 MPH changeup to Jason Kipnis — a career 112 wRC+ hitter. The fourseamer immediately prior to this changeup was thrown in almost an identical location of the strike zone — showing Rosenthal’s repertoire is ripe for the benefits associated with pitch tunneling.

This takes us to the all-important “third pitch.” While I believe Rosenthal could be successful — yes, even as a starting pitcher — with two primary pitches, having a third pitch that is more than just a mere “show” pitch will most definitely make things a bit easier for him. From a tunneling perspective, the slider could be absolutely huge for the aspiring starting pitcher (curveballs, while effective at changing speeds, aren’t good for tunneling purposes). Returning to the repertoire table above, you will see that the slider’s magnitude of movement is almost exactly the same as his fourseamer’s, only breaking to his glove-side rather than his arm-side. At 97-98+ MPH, the batter must commit to the fourseamer very early on, and if Rosenthal is tunneling a slider that will eventually break six plus inches the other way, he will be breaking and/or missing bats on a regular basis.

Bottom line, I understand that we have essentially three scoreless innings against the Pittsburgh Pirates last October to work with when envisioning Rosenthal as a starting pitcher. As I stated earlier, that is nowhere near enough to predict his ability to manage a starter’s workload. However, when the primary replacement option is an inconsistent Wacha (I’m not about to get as excited about one spring training bullpen session as apparently Matheny already is), I’m more than willing to take a legitimate chance with Rosenthal. Of the in-house options, Rosenthal’s repertoire most resembles that of Reyes. If the trial doesn’t work out, move him back to the bullpen. Considering he already throws primarily out of the stretch, it’s not like he is going to forget how to pitch in relief. Plus, any further developments to his repertoire — something that will happen in the process of being stretched out — will only be beneficial in the long-term, regardless of his ultimate role with the Cardinals.