Of the three arms competing for the fifth spot in the Saint Louis Cardinals rotation, the strongest belongs to right-hander Trevor Rosenthal. However, that doesn’t mean he’s best suited for a spot in the starting rotation–yet.
Last year, after being called up from Triple-A in the middle of July, Rosenthal thrived in the bullpen. He posted a 2.78 ERA (3.09 FIP) in 22.2 innings and blew away nearly 10 hitters per nine innings with a fastball that averaged 97.5 MPH. Who cares if division rival Cincinnati Reds had Aroldis Chapman, the Cardinals found their own fireballer.
Rosenthal throws his fastball 80 percent of the time which is a bit much for a starting pitcher. You want to have at least one other power pitch to go with your put-away. Rosenthal’s fastball could double as his put-away (which drew an almost 11 percent swing/miss rate) he will have to develop a change-up as well as his curve that he threw 11.7 percent of the time.
In the Minor Leagues, Rosenthal threw a high of 121 innings of Single-A ball in 2011 and 108.2 in 2012 between Double-A and Triple-A. His large workload in 2011 resulted in an inflated 4.11 ERA (3.04 FIP) and going 7-7 in 22 starts. The next year things got a bit better with an ERA of 3.49, though his hot start in Double-A gained him a promotion to Triple-A. That promotion saw his ERA jump almost one and a half runs.
Rosenthal definitely needs more grooming in the minor leagues if he’s to become a future starter. But for now, he’s best suited to be Jason Motte‘s setup man–with all due respect to Mitchell Boggs. The Cardinals should let him continue to shut down hitters late in games–as you know, Saint Louis fell victim to many opponents in late inning rallies–while giving him the occasional start should one of the members of the rotation go down with an injury.
Shelby Miller is likely going to get the last rotation start–barring a horrendous March as well as a returning shoulder condition–so it makes sense to keep Rosenthal in bullpen to boost an already strong relief squad.