Fixing Trevor Rosenthal

One year ago, Trevor Rosenthal was an All-Star closer for the St. Louis Cardinals after posting an extraordinary fWAR of 2.1 -- good enough for fourth highest among qualified MLB relievers -- over 68.2 innings pitched. So far in 2016, Rosenthal has been a negative contributor out of the bullpen at -0.1 fWAR through 26 innings over 31 appearances. His manager has since removed him from the closer role as he works to get back up to his 2013-2015 level of performance. Rosenthal may have allowed two hits in last night's scoreless inning against the Kansas City Royals, but his approach -- I will explain this further below -- was nearly perfect (the lone obvious flaw being a hittable, lower-in-the-zone fourseamer on 0-2 versus Salvador Perez). If he is able to replicate said approach, he should be back on track sooner rather than later.

I have said it before and I will say it again, but if the Cardinals want to be competing for a playoff spot come late August-September, they better hope Rosenthal has performed well enough to be reinserted into the closer role (full disclosure: I know the "closer role" is silly, but I also understand that it is likely not going anywhere). Rosenthal's repertoire potential is just too flashy to stay this dull for long and limiting a repertoire of this quality to set-up or mop-up duties simply does not seem optimal. I understand that Seung Hwan Oh has been very good (1.3 fWAR) since joining the Cardinals, and he obviously has past closer experience, but his most value comes from being a flexible, utility-type set-up man. Plus, sometimes the highest leverage innings occur before the ninth inning, so it is reassuring to have a reliever of Oh's quality available for such instances.

2016 Statistics

The easy answer to "Fixing Trevor Rosenthal" is two-fold: 1) Walk fewer hitters and 2) Grind through plate appearances while waiting for that unbelievably unlucky .453 BABIP to regress toward the 2016 league average of .300. However, easy answers are not very fun, and they do not really provide specific adjustments that can be made. If I wrote a post solely dedicated to the statement that Rosenthal needs to walk fewer hitters, I would sincerely expect (and welcome) backlash because duh, his walk rate is the second highest among MLB relievers (behind former Cardinal farmhand Kyle Barraclough). Instead, I plan on addressing two specific adjustments that simply must be made -- two adjustments that I saw flashes of in last night's outing.

1) Elevate the Fourseamer

Heatmaps via BrooksBaseball.net

The PitchF/x component of Rosenthal's fourseamer remains essentially unchanged. Velocity is down a touch (97.76 MPH versus 98.55 MPH), but Rosenthal has made it a habit to dial the fourseamer up as the season goes along, and he touched 100.2 MPH last night, so velocity should be the least of our worries. Fox Sports Midwest Broadcaster Al Hrabosky made a comment on last night's telecast to the effect that the Rosenthal's fourseamer has been straighter in 2016 compared to previous seasons. Upon further review, this appears to be a factually incorrect statement as Rosenthal's fourseamer has displayed more horizontal movement this season (-5.69 inches) than it did in both 2013 (-2.81 inches) and 2014 (-2.76 inches).

What has changed is the way Rosenthal has located his fourseamer. Prior to the 2016 season, Rosenthal climbed the ladder (see the area boxed in yellow) with his fourseamer 41.52% of the time. So far this season, his fourseamer has landed in this zone only 36.96% of the time -- a decrease of four and a half percentage points. The difference may appear to be slight, but when dealing with the small sample sizes inherently associated with relievers, even the smallest change can prove to be impactful. What's important to remember about Rosenthal's ability to climb the ladder is that when he does, hitters often swing and miss. When his fourseamer stays down (a location desirable for pitchers with much less potent fastballs), it becomes much more hittable.

Heatmap via BrooksBaseball.net

Revisiting last night's outing, Rosenthal threw 15 fourseamers, and 13 of them were up in the zone. Once BrooksBaseball's heatmaps update, all 13 will comfortably fall in the yellow-boxed area shown in the two heatmaps above. What was the end result of 13 fourseamers being up in the zone? Five whiffs for a very impressive whiff rate of 33.33%. Rosenthal's career whiff rate on his fourseamer? 13.05%.

2) Please, Just Trust the Changeup Already

Rosenthal has a very good changeup. In fact, Rosenthal probably has one of the best reliever changeups in all of baseball. Yet, in 17 appearances this season (54.8% of total appearances in 2016), Rosenthal has gone to the pitch two times or fewer. The sample size is incredibly small (74 pitches thrown, excluding last night), but the pitch's pertinent outcomes have been very good thus far. Hitters continue to swing and miss at the pitch, and when they do manage to put the ball in play, three out of four times it has gone for a ground ball. Not to mention the pitch, when thrown down in the zone, is a perfect complement to his fourseamer up in the zone. Just ask Eric Hosmer about his strikeout last night:

Pitch number five was a 100.1 MPH fastball up and in on the hands. Pitch number six -- the strikeout pitch -- was an 88.7 MPH changeup diving down, away, and out of the zone (I really should have this two-pitch sequence GIF'd and subsequently tweeted directly to Rosenthal because it was perfect).

Bottom Line

Rosenthal absolutely needs to walk fewer hitters. Duh. That should go without saying. However, as documented above, if he begins to focus on locating his fourseamer up in the zone and begins to throw his changeup at the very least three times per outing, he will soon be on the path to his 2013-2015 level of performance. Oh, and this doesn't even mention that, last night versus Paulo Orlando, he flashed the ability to throw a get-me-over slider, a perfect weapon for 0-0 counts.