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The ups and downs of the 2014 season for Trevor Rosenthal

Trevor Rosenthal has had a relatively inconsistent 2014 season. Let's take a look at some PITCHF/x data and see what we can find out.

Michael B. Thomas

After accumulating 2.2 fWAR in the regular season and then throwing 11 and 2/3 postseason innings without allowing a single earned run in 2013, expectations were extremely high for Trevor Rosenthal this season. Well, as Michael Baumann noted in this somewhat controversial piece for Grantland, "Closer Trevor Rosenthal hasn't quite lived up to expectations." Given the majority of expectations were probably unfair for a 24-year-old pitcher entering just his second full season as a big leaguer, I guess Baumann is not necessarily wrong. However, despite having up-and-down periods scattered throughout 2014, bottom line statistics (see below) show that though this season has been a significant drop-off from 2013, it should not be viewed as the obvious negative Baumann portrayed it to be.

K% BB% ERA FIP Saves
March/April 31.6 12.3 4.73 3.20 7
May 30.4 12.5 3.46 2.12 9
June 27.5 17.7 0.75 3.29 8
July 28.0 6.0 3.97 1.98 8
August 23.6 20.0 4.76 4.89 8
September 30.3 12.1 1.13 2.13 4
1st Half 29.3 13.6 3.50 2.85 28
2nd Half 27.0 13.5 2.84 3.16 16
Total 28.5 13.6 3.26 2.97 44

Though the bottom-line numbers are good and his FIP is actually estimated as "excellent" per Fangraphs, no one can deny the disparity to the numbers he produced in 2013 (34.7 K%, 6.4 BB%, 2.63 ERA, 1.91 FIP). Plus, his month-to-month consistency has been lacking (i.e. a very poor August sandwiched by a solid July and September), something he did not have to worry about last season. Thus, what has been different for Rosenthal in 2014?

One theory behind Rosenthal's inconsistent 2014 performance has been brought up in VEB comment threads on I believe two separate occasions, and it was even included in the form of this fanshot. Chris O'Leary (also known as thepainguy, VEB member since 2008) believes that "part of the problem is that he has been throwing a cutter"—conveniently classified by Chris as "Accidental Cutter Syndrome." Chris studies baseball mechanics (both pitching and hitting) much more than I do. He has gathered enough evidence and performed enough case studies on mechanics that he is able to run his own website dedicated solely to this type of subject matter. Thus, when he hypothesizes something related to mechanics, especially on multiple occasions, I tend to take notice.

Yet, I didn't just blindly take his word for it on this particular occasion, especially because BrooksBaseball (specifically Harry Pavlidis) has yet to classify a single fastball from Rosenthal as a cutter in his major league career. With PITCHF/x data readily available, I did some pretty intense data collection on Rosenthal fastballs, and the following table includes what I came up with. First, to make sure everyone is on the same page, glove-side run from a right-handed pitcher is synonymous with cutter movement. Arm-side run from a right-handed pitcher (also known as tailing action) is commonly achieved on fourseam fastballs (slightly), twoseam fastballs, and changeups.

Glove-side run (cutter movement, #) Arm-side run (tailing action, #) Arm-side run percentage
March/April 34 105 75.5%
May 9 159 94.6%
June 9 169 94.9%
July 12 171 93.4%
August 18 154 89.5%
September 5 84 94.3%
Total 87 842 90.6%

As you can see, Rosenthal has thrown 87 fastballs with glove-side run in 2014, compared to 842 with arm-side run. Given his fastball averages 1.73 inches of arm-side run (tailing action), the fact that 90.6% of his fastballs move in that direction is not surprising. In the middle of a discussion spurred by Rosenthal's blown save (six on the season) on Tuesday night against the Brewers, Chris reasonably responded to Ben, "You're not going to see [the reasoning behind Rosenthal's inconsistency] by looking at averages. It's only going to stand out by going pitch by pitch." Thus, this is exactly why I took the time to manually look at every single Rosenthal outing, pitch by pitch, from 2014 for the data included in the table above. For perspective, Rosenthal's arm-side run percentage was 92% in April 2013 and 94.6% in his dominant October 2013. Though both are slightly higher than his percentage in 2014, it is difficult to determine whether or not this is significant.

Another thing Chris brought up was that the times he picked up on Rosenthal's cutter arm action (i.e. following through on the outside of the ball, instead of through the ball), Trevor had a decrease in command and velocity. For this post, I am not going to look at command because there are far too many variables that go into that (including his off-speed pitches), but I did look at fastball velocity. In appearances in which Rosenthal threw at least three fastballs with glove-side run (13 total), his fastball velocity averaged 98.09 MPH and topped out at 99.6 MPH. Thus, even when Rosenthal was struggling to repeat a consistent, through-the-ball release of his fastball, data shows it didn't negatively affect his overall velocity.

Thus, 153 games into the 2014 season, we have seen some flashes of "2013 Rosenthal," but we have also seen numerous instances where he looks like he just cannot find the strike zone. After pretty extensive data review, I am pretty confident that "Accidental Cutter Syndrome" is not what ails Rosenthal's consistency. I'm not so sure the often-brought-up "drop" in velocity can be blamed either—check out his average fastball velocities, month-by-month, dating back to the beginning of last season. Instead, I believe Rosenthal is merely slumping at times, not abnormal for a 24-year-old sophomore big leaguer. It doesn't help that he has walked the first batter he has faced seven times and the first batter of an inning eight times in 2014. One thing I am certain about, though, is that Rosenthal will play an integral role in the final regular season push, and if the Cardinals intend on making a deep run in the playoffs, they'll need him shutting down game after game after game, just like he did in October 2013.

Credit to BrooksBaseballFangraphs, and Baseball-Reference for the data used in this post.