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St. Louis Cardinals: Could Trevor Rosenthal Factor in the Starting Rotation?

Trevor Rosenthal St. Louis Cardinals

With news that Alex Reyes will undergo Tommy John surgery, the St. Louis Cardinals starting rotation is probably set. Michael Wacha should handle the fifth spot in the order come opening day.

Now, the question is what happens if another pitcher goes down. The Cardinals are counting on an aging Adam Wainwright, who has a spotty health record himself. Additionally, St. Louis is betting on a Tommy John comeback from Lance Lynn. Lastly, the team needs a healthy year from Michael Wacha, who has a troubling history of breaking down. One (or more) of these dominoes will likely fall during the season, or perhaps even earlier. A given pitcher has a 40% chance of spending time on the DL in a season. Consequently, there’s about a 66% chance at least one of five in a rotation spends time injured.

The Cardinals have a few backup options. Luke Weaver tore his way through the Minor Leagues before a lackluster MLB debut. John Gant has had similar success in his MiLB career, but also struggled in his first taste of MLB action. While these two are passable, they’re not inspiring options.

Enter Trevor Rosenthal. While most of us have become accustomed to his fastball only, nerve-wracking relief appearances, he used to be a starting pitching prospect, and a very good one at that. Baseball America ranked him the best pitching prospect in the Texas League in 2012 before slotting him 39th in the 2013 Top 100.

In that ranking, BA rated his fastball, changeup, and curveball at grades 75, 55, and 50, respectively (50 equates to MLB average). His control graded as 55 and his command at 50. Based on this assessment, “MiLB starter” Trevor Rosenthal had two above average pitches and an average curve, a repertoire projected to transition smoothly to the MLB starting rotation.

This assessment is consistent with various other reports I’ve been able to dig up. Additionally, Rosenthal commented back in 2012 that he was adding a cutter that might have always been more of a slider, which FanGraphs noted was “better than average.” Taken at face value, it would appear that Trevor Rosenthal could be a candidate to start should the need arise in 2017.

Of course, Rosenthal is five years removed from starting games at all. While the St. Louis Cardinals indicated early in the offseason that they planned to stretch Rosenthal out, that will probably take more time than just Spring Training. Even as a starter in the Minor Leagues, he averaged only slightly more than five innings per start.

In addition to that obvious issue, I don’t think Rosenthal’s repertoire plays as well as it’s rated. From videos I’ve found, his curveball and cutter/slider just haven’t missed many bats, even at the Minor League level. His whiff rate on the slider is only 11.3% for his MLB career. Even worse, his curve comes in at only 6.0%. That’s terrible. Neither move much horizontally or vertically, and hitters appear to have no problem picking them up.

His move to the bullpen reduced the need for either of these pitches. In relief, he’s a two pitch guy, using a fourseamer or changeup on more than 90% of his pitches. He rarely flashes the curve or slider, and it’s usually not good when he does. It would be, at the very least, optimistic to think he could fake a three-pitch repertoire as a starter.

On a positive note, the two pitches he does use are very good. Over his career, batters have managed a 106 wRC+ against his fastball and a negative 2 wRC+ against the changeup.

His command also appears to be less of an issue than my eye test believed. His Zone% of 47.0% since the start of 2013 ranks 90th of 507 pitchers with more than 100 innings, placing him in the top 20%. Among starters, that Zone% would rank 38th of 280 pitchers.

While his career walk rate of 10.3% is high, his strong 30.1% strikeout rate helps mitigate the potential damage. As a starter, he might see both of those numbers drop slightly to mirror the 25.0% K% and 8.6% BB% he had in 2011 and 2012.

His command is observable when breaking down his location heatmaps, available at Baseball Savant. Trevor Rosenthal works his fastball consistently up-and-away to righties (right heatmap). Against lefties, he has a similar approach with slightly worse execution. He commands his changeup well, working it low on one side of the plate, inside to RHHs and away from LHHs (left).

Trevor Rosenthal St. Louis Cardinals Trevor Rosenthal St. Louis Cardinals

Further, platoon splits are not a problem for Trevor Rosenthal. He owns a career .263 wOBA versus lefties, compared to a .310 mark against righties. While the sample size is less than 300 innings, it’s fair to expect Rosenthal to be equally effective against hitters on both sides, which would help him transition to a starting role.

Much of Rosenthal’s struggles at the MLB level can be traced to his .338 career BABIP, including a career worst .425 mark last year. Steamer and FanGraphs Depth Charts see this rate declining to .283 and .300, respectively, which mirrors his .292 mark in 2011 and 2012 as a full-time Minor League starter. Personally, I think it’s more likely to expect a BABIP near his .338 career level.

Overall, I’m not terribly excited about the prospect of Trevor Rosenthal as an MLB starter. I don’t envision him being much better in the rotation than Luke Weaver. Rosenthal has a much higher ceiling in the bullpen, which he has proven since 2012.

However, we don’t always get to be picky about these sorts of things. If injuries force the St. Louis Cardinals to let Rosenthal start, we’ll have to sit back and hope for the best.

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