Adam Warren was one of the biggest surprises for the Yankees in 2014 pitching out of the bullpen. He had a 2.97 ERA and a 3.28 xFIP and stabilized the middle innings before the Yankees got to Dellin Betances and David Robertson later in the game.
The biggest surprise with Warren was his added strikeouts and velocity coming out of the bullpen. Even though that will generally happen with most pitchers who go from starting to relieving, it was especially noticeable with Warren because he also relieved in 2013 and never showed this kind of stuff. According to Brooks Baseball, Warren averaged 95.28 MPH on his fastball after averaging 93.97 MPH in 2013 and his K/9 jumped to 8.69 last year from 7.48 the previous season.
Even after Warren's great season in the bullpen last year, returning him to the rotation must be considered this year due to the Yankees' lack of depth in their rotation. Top pitchers Masahiro Tanaka, Michael Pineda and CC Sabathia are all health risks, and Chris Capuano is a performance risk at the fifth spot. The first candidate to replace an injured starter would seem to be Bryan Mitchell, who has limited MLB experience.
Meanwhile, the depth in the Yankees bullpen is fantastic with new additions Andrew Miller, David Carpenter, Justin Wilson and Chasen Shreve. Carpenter can essentially replace Warren's 7th-inning role from last year and be just as productive, so it makes sense to give Warren the opportunity to see if he can start again effectively in Spring Training. If it does not work out, he could easily go back to the bullpen with no harm and no foul. The question is, can he take what he did out of the 'pen and make it as a starter again?
In addition to the increased velocity, another big reason Warren succeeded out of the bullpen was that he trusted his stuff and was not afraid to challenge hitters. His walk rate fell from 9.1 percent in 2013 to 7.4 percent last season. If that continues, it will help keep his pitch count down as a starter.
One reason to think Warren could return to being a starter successfully is that he still used three pitches out of the bullpen. He threw his fastball 35.8 percent of the time, his slider 33.1 percent and his changeup 16 percent. He even mixed in a curveball 9.2 percent of the time. As his third pitch, the changeup will be key if he returns to starting. Starters need that third pitch to make it around the lineup the second and third time. Warren's changeup was very effective last year, as batters only hit .167 against it with a .093 ISO. His slider was even better, arguably his best pitch last season. He had a 15.5 percent whiff rate on it and batters only had a .219 batting average with a .088 ISO against it.
After one disastrous start in 2012, the Yankees made Warren a reliever in 2013, and he's only made two short starts since then. We really don't have much data to evaluate him on starting at the MLB level. The fact that his slider and changeup have both been very good secondary pitches for him as a reliever should indicate that he can succeed as a starter, but Warren hit a big wall in June, July and August last year, so it remains to be seen if the quality of his stuff can hold up over seven innings per game and over 200 innings per season. If he can do that, he has the capability to be a decent mid-to-back end rotation piece. Obviously, the Yankees aren't going to pitch him 200 innings this season after only 78.2 innings last year, but if he were to remain a starter over the next few years he would have to get to that point.
Even if Warren just gave the Yankees quality starting innings until Ivan Nova comes back, that would be a win. It's hard to see Capuano giving them what he did last year, and Warren could easily go back to the bullpen and wait for the inevitable injury to crop up if it had not already done so. That would be a way to keep his innings down while also bolstering the rotation depth. What the Yankees do with Warren is definitely a top story to watch when camp opens.