The St. Louis Cardinals entered spring training with four spots in their starting rotation already taken, and three young pitchers - Shelby Miller, Joe Kelly and Trevor Rosenthal - battling for the final available spot. They were relatively open about the scenario and the fortunate position in which they found themselves. After a few weeks of spring training, we are beginning to see the pieces of this puzzle fall into place.
Cardinals GM John Mozeliak announced this week that Rosenthal was no longer a candidate in the race, but also adding that he "would be shocked if [Rosenthal] didn't make the major league team," according to Rick Hummel of The St. Louis Post-Dispatch. SImply put, the Cardinals anticipate Rosenthal being extremely good as a reliever, and doing so extremely soon, and given that they have plenty of other options in their starting rotation, there's no sense in risking Rosenthal's arm or development by forcing him to work as a starter any longer.
A different organization might be trying to squeeze the most value out possible out of Rosenthal's powerful arm, but the Cardinals have the luxury (one they've created for themselves) of using Rosenthal in a way they can be almost certain he will be successful instead of trying to get more out of him. There are risks to pushing a prospect further - arms don't always respond well to the starting workload (especially a converted position player like Rosenthal who doesn't have an amateur career of starting games built up in his arm). Additionally, the Cardinals likely see Rosenthal as a back-end reliever, someone who will be pitching in crucial late-inning situations. While talent-wise, he should be ready to slide into that role soon, there is some mental development that is required to learn how to handle the pressure of those situations.
Clarifying Rosenthal's role now will allow him to focus on his task at hand and train his arm to pitch shorter, more frequent, stints out of the bullpen. Because they have the luxury of having additional young starters, this is a good decision by the Cardinals.
The rotation battle remains Miller's to lose, and he did nothing to change that on Friday, throwing "three strong innings" against the Nationals regular lineup, says Derrick Goold of The St. Louis Post-Dispatch. Despite Kelly having more major league experience, Miller is the better pitcher and is major league ready himself. Kelly could also find himself in the Cardinals bullpen, but he could also serve as a stopgap in the rotation if the Cardinals want to keep Miller in the minors for a few months, although they have shown no signs of wanting to do so.
Even if Miller wins the 5th spot, Kelly should get some starts this season. Rotations rarely make it though the entire season with just five starters, and that's even less likely when one of them is a rookie, and the other is Jaime Garcia, who is coming off of an injury.