The 2016 St. Louis Cardinals bullpen constructed to conserve the arm of Trevor Rosenthal

Earlier this morning, Alex Crisafulli published our third installment of the 2016 Viva El Birdos projections project, this one centered on St. Louis Cardinals closer Trevor Rosenthal (in case you missed them from earlier in the week: Matt Carpenter's and Jhonny Peralta's). This turned out to be good timing given that I had already been planning on writing about the All-Star closer for the VEB Daily slot (publishing one hour after his post).

Since the start of the 2013 season, there are only three relief pitchers in all of Major League Baseball (Tony Watson, Mark Melancon, Bryan Shaw) with more regular-season innings pitched than Trevor Rosenthal (214.1 IP). Including the postseason, Rosenthal's inning total climbs to 231.2 IP (or ~77 innings per season). Further, courtesy of BrooksBaseball.net, the flame-throwing righty has thrown 3,980 pitches during that time, with nearly 3,100 (~77%) being fourseam fastballs at a near-league-leading average velocity of 98.16 MPH.

Mechanically speaking, Rosenthal is quite sound, so generally speaking, one should not be too worried about a specific arm action predisposing the 25-year-old righty to a throwing arm injury. However, Rosenthal throws very hard, and when it comes to pitcher injuries, we tend to worry more about those who throw at a high velocity than those sitting in the 88-92 MPH range due to increased stress and workload put on the arm and shoulder. One needs to look no further than some stillshots of the arm just before release point to get the picture.

With Rosenthal being an integral component of the bullpen, and frankly, one of the best relief pitchers in baseball, it would be wise to conserve his arm in 2016 so that he remains healthy and is as fresh as possible come October, especially if the Cardinals are unable to win the division and are forced to compete in the dreaded Wild Card game, also known as a mere coin flip. I like the Cardinals' chances much more if Rosenthal is able to go two innings in such an important game than being limited to a maximum of one.

It was pretty clear last season that manager Mike Matheny placed his trust in basically three relievers: Rosenthal (duh), Kevin Siegrist, and Seth Maness. Those three will again play important roles in 2016, but the addition of Seung-hwan Oh, the re-signing of Jonathan Broxton, and the potential emergence of borderline-MLB-ready Sam Tuivailala should, theoretically, lighten the workloads of Rosenthal, Siegrist, and Maness. This scenario does not even include Jordan Walden, the primary set-up man in 2015 before suffering a season-ending shoulder injury, who may or may not be healthy again.

On conserving Rosenthal

As you can read about in this leverage index primer on FanGraphs, gmLI is the average leverage index when a pitcher enters the game. Unlike some statistics, interpreting gmLI is pretty self-explanatory: any value 2.0 or greater is considered "high leverage," anything from 0.85 to 2.0 is "medium leverage", and finally, anything below 0.85 is considered "low leverage."

To make gmLI even clearer, I will now bring up two of Rosenthal's games from the 2015 season, one that was high leverage and one that was low leverage. On September 20th, against the rival Chicago Cubs at Wrigley Field, Rosenthal entered the game in the bottom of the ninth with the Cardinals leading 4-3. This appearance warranted a gmLI of 5.16, well above what is considered high leverage. At the other end of the spectrum, on September 5th, Rosenthal was called upon to shut the door on the Pirates in a 4-1 game, and predictably the gmLI fell comfortably into the low leverage classification at 0.26.

Using gmLI as a very rough guide, over the last three seasons, 33.2% of Rosenthal's appearances have come in low leverage situations (gmLI 0.00 to 0.85), with 17 occurring in 2015, 22 in 2014, and 32 in 2013. This is a promising development, though, considering each season has seen a decline in low-leverage appearances (I realize we are only talking about three seasons of data here). Plus, Rosenthal has been appeared in fewer games (74 to 72 to 68) and has thrown fewer innings (75.1 to 70.1 to 68.2) in each subsequent season as well.

Considering Rosenthal still ranks fourth among relievers in innings pitched since 2013, there is still work than can be done to conserve the closer. Now, I do not expect Matheny (or one of his assistants) to somehow utilize the intricacies of leverage index when making the in-game decision on whether or not to use Rosenthal. Rather, it is much easier than that (with caveats explained below).

If the Cardinals enter the ninth inning with a three-run lead, Matheny should seriously consider using an option other than Rosenthal. He now has four (and eventually five when Tuivailala is called up) relievers with experience as a closer. While none are as effective as Rosenthal, they are more than capable of shutting the door, particularly in low-leverage situations with wider margins for error.

As with anything in baseball, there are obvious caveats to this thought process. If the wind is blowing out at Wrigley, and Kyle Schwarber, Anthony Rizzo, and Kris Bryant are due up, I understand going with Rosenthal. If Rosenthal goes multiple days without work, then get him in a game or two to keep him sharp. Or, most importantly, if a Cardinals win guarantees the National League Central crown, I understand using Rosenthal in a three-run game.

Regardless, Matheny now has tools at his disposal to conserve not only his All-Star closer in Rosenthal but also other heavily-worked relievers in Siegrist and Maness. Based on interviews I have heard from the manager thus far in spring training, I can hear the excitement in his voice when discussing his bullpen. I hope he successfully acts on this excitement by being more efficient with his most effective bullpen arms in 2016.