Despite the New York Yankees' incredible return from the Chicago Cubs for essentially two to three months of All-Star closer Aroldis Chapman, the St. Louis Cardinals should resist the urge of trading former All-Star closer Trevor Rosenthal at this time. Why, you ask? Because it would be the ultimate case of selling low, especially considering the fact that general managers are currently making deals in a sellers' market. From a performance standpoint, 2016 has, without a doubt, been nothing short of a forgettable season for Rosenthal, bottoming out the day he was replaced as closer by Seung Hwan Oh (and could somehow reach down even further should he ever be demoted to Triple-A Memphis).
That being said, Rosenthal, who just turned 26 at the end of May, is under team control through the 2018 season. Given the return for Chapman, two years of control in addition to two to three months of Rosenthal should require a pretty hefty package itself. Unfortunately, we are talking about a "what have you done for me lately?" league with the baseball minds in charge also having a pretty solid grasp of the term "reliever volatility" (see Jonathan Broxton and Steve Cishek for prime examples).
This means that, despite Rosenthal being in the top 10 of reliever fWAR since the start of the 2013 season (remember, this includes zero help from his 2016 goose egg thus far), there is a good chance the Cardinals would be forced into settling on a much less attractive package from an eventual trade partner (Indians, Nationals, Giants, and mystery team?). Not only can teams leverage Rosenthal's underperforming statistics into trade talks, but they can also mention the fact that Rosenthal's own team removed him from the closer role. Being okay with selling low on Rosenthal is in turn accepting a hot-take position that he merely forgot how to pitch and that there are no positive signs regarding his future. To flatly rebuke this stance, let's first take a look at some of Rosenthal's 2016 statistics, as compared to his career statistics:
There are three columns to consider when reading this table: BB%, HR/FB%, and BABIP. First, Rosenthal's walk rate of 16.2% is the absolute highest it has ever been as a professional -- two and a half percentage points higher than 2013 (13.6%) and roughly six percentage points higher than its highest while he was pitching in the minor leagues (he posted a 9.8% walk rate with Double-A Springfield in 2012).
The ballooning of Rosenthal's walk rate is somewhat complicated because he is actually throwing pitches in the strike zone more frequently this season than he ever has with a zone rate (Zone%) of 52.9%, as compared to his career average of 50.6% and previous high of 51.4% in 2013. However, the 26-year-old righty is inducing fewer swings on pitches outside of the zone, reaching a career low out-of-zone swing rate (O-Swing%) of 25.4%, compared to a career average of 30.0% and previous low of 29.0% in 2014. The magnitude of difference between his drop in O-Swing% outweighs his rise in Zone%. Regaining confidence in his offspeed pitches should help bring his O-Swing% back to where it should be based on his career average.
Next is HR/FB%, which, again, has reached a career high for Rosenthal. Prior to 2016, Rosenthal was one of the league's very best relievers at keeping fly balls in the ballpark. And despite a very sharp increase this season, there are still 47 qualified relievers with a higher HR/FB% than him. Thus, while Rosenthal may not return all the way to his 2013-2015 form (4.8%, fourth best in MLB), he definitely has room to improve, which, to me, should be viewed as a potential positive. If his ERA was above five (as it is now), and his HR/FB% was relatively close to his career rate, this would actually be considered a negative.
Finally, the dreaded BABIP column. It is July 26th (with ~60% of the regular season complete), and there is only one relief pitcher in all of baseball with a BABIP north of .400 and his name is Trevor Rosenthal. What's worse is Rosenthal's BABIP has crept nearly all the way up to the halfway point between .400 and .500. Using his career average of .337 as a guide (despite not yet reaching the 2,000 balls in play stabilization point), we understand that Rosenthal has no business possessing such an extreme BABIP (the 2016 reliever league average is .295).
BABIP is dependent on two things: defense and luck. We all know the Cardinals' defense has been shaky this season, but not this shaky, so it appears that Rosenthal continues to be a victim of some extreme bad luck. I despise using luck as a crutch in baseball analysis, but when you are dealing with a BABIP that has never been seen before (the closest was .410 by Jose Mijares in 2013), you cannot help but bring it up. The BABIP against Rosenthal will regress, but if he wants to help out with the recovery process, I recommend moving his fastball out of the middle of the strike zone.
Rosenthal has not been good this season. This is a fact. However, there are ways in which he can improve his approach, and there are inflated statistics (BB%, BABIP, HR/Fb%) that will almost certainly regress on their own. While returning to 2015 form is not necessarily likely at this point, selling low on Rosenthal now when there really isn't a long-term high-leverage reliever anywhere close in the minor leagues makes very little sense. John Mozeliak and the Cardinals should remain focused on adding to the bullpen, not taking away from it.