We know about the issues with the Yankees' starting rotation as it stands right now. It's lost four of its top six members from 2014 according to fWAR. Masahiro Tanaka, Michael Pineda and CC Sabathia all battled serious injuries last year. Nathan Eovaldi will need more swings and misses as he transitions from the NL to the hitter-friendly AL East, and Chris Capuano at 37 hasn't been an every fifth day regular for anyone since 2012. We also know that the Yankees' bullpen looks like a powerhouse heading into 2015. Newly acquired human K-counters Justin Wilson and David Carpenter will try and set the table for Andrew Miller and Dellin Betances who were two of baseball's top seven relievers in fWAR, FIP and K-rate. Later-season contributions from near-ready prospects like Jacob Lindgren, Nick Rumbelow and Chasen Shreve could make the unit even stronger.
Should the Yankees tap into their strength to find a possible solution for a probable weakness? At 27, Adam Warren figures to have a key role in the retooled pen, but he spent his entire minor league career as a starter, and he wasn't bad at it. Between being selected in the fourth round of the 2009 draft and ascending to the big league bullpen in 2013, Warren managed a 3.11 ERA and a 1.26 WHIP across four levels of the Yankee farm system. He logged 305 AAA innings in 2011 and 2012, so his workload wouldn't need to be heavily limited as a fifth starter. Warren acts more like a starter than a short reliever in that he makes use of four different pitches. Whereas more typical late-game arms like Betances, Miller and Carpenter are almost exclusively fastball-slider, Warren went to the heater at a less-than 50% rate in 2014, while routinely mixing in a slider (32.9%), a change (16.2%) and a curve (9.4%). All that in mind, there's a solid case to be made that he's a better bet than Capuano or Bryan Mitchell, whose minor league numbers have yet to level up with the superior stuff that he flashes.
So why not let Warren compete for a rotation spot this spring? Since moving to the pen, he's made improvements that might not translate to longer outings. After sitting in the low 90's in college and the minors, Warren's been able to increase his fastball velocity as a reliever. He started off 2013 - when he pitched mostly in long relief averaging 2.16 innings per outing - hitting 92.9 mph with his four-seamer in April and finished the year at 94.8 mph. His growth continued as a setup man in 2014 and by September, the same pitch was averaging 95.4 mph. Although the fastball was his most hittable pitch, the better zip allowed him to set up his secondary pitches more effectively. Last year, he held opposing hitters to a 35 wRC+ against the change and a 67 wRC+ against the slider. Warren's overall performance in the setup role dwarfed what he did as a starter, at least at the AAA level, where he had stalled somewhat, posing FIPs of 4.09 and 3.68 and K-rates of 6.56 and 6.31 in his two seasons there. As a reliever in 2014, Warren was impressive with a 2.89 FIP, a 1.10 WHIP and an 8.69 K-rate.
The decision of where to use Warren this season comes down to whether the extent to which he'd be better than Capuano, Mitchell, or eventually a rehabbing Ivan Nova outweighs the loss of him as a very good reliever. While his solid control and versatility might make him a workmanlike back-end option, he's unlikely to be anything more than that, especially if his fastball dips back toward its low-90's origins. It's debatable whether that sort of output justifies jeopardizing the comfy niche Warren's carved for himself in the pen. While he might rank behind Betances, Miller and probably Carpenter and Wilson on the depth chart, it won't hurt Joe Girardi to have more right choices, especially if Capuano and Eovaldi, who has averaged fewer than six innings per start for his career, wind up comprising two-fifths of the rotation.
The Yankees seem to be all about the long run these days, and in that long run, it's wiser to put players in the position that maximizes their skills, not the one that desperately plugs and immediate need. There's no reason not to stretch Warren out this spring - just in case - and there may arise some nuclear winter scenario where the Yankees have no choice but to have him start games. But if that doomsday doesn't come about, they're better off letting him build on what could be a promising bullpen career.