Ivan Nova's career has definitely been a roller coaster ride. As a teenage prospect, he spurned advances from the rival Red Sox because he was a Yankee fan. His childhood team signed him in 2004, only to let the Padres snatch him up in the 2008 Rule 5 Draft. Two teams ended up making the same mistake by giving up on Nova, and the Padres sent him back to the Yankees.
During his first start, he accidentally let a pitch sail above the head of Toronto's then MVP candidate Jose Bautista before basically daring him to do something about it. In 2011 and 2012, he was wildly inconsistent, but managed to demonstrate an ability to get a decent amount of groundballs. After a rough start to 2013, he was sent down to the minors, before being recalled to start the June 23 game against the Rays. From that point to the end of the season, it looked like Nova finally put it together, with a 2.70 ERA in 116.2 innings.
Despite the encouraging stretch, Nova's .288 BABIP and 82.1% LOB% were both causes for skepticism. In 2014, he got shelled to the tune of an 8.27 ERA before doctors realized he had torn his UCL and needed Tommy John surgery.
Even without a surgically repaired elbow, Nova's true ability is very hard to pinpoint. His post-recall 2013 stats did have their question marks, but they also were also impacted by changes in his pitching style. Not only did Nova completely scrap his slider, he also began integrating a sinker, as shown by this chart from Brooks Baseball:
In addition to ditching his slider for his sneaky-good curve, which generated a 46.9% Whiff/Swing rate in 2013, his sinker was also very good. According to the Baseball Prospectus Pitch F/X leaderboard, Nova's sinker was 15th in Whiff/Swing rate and 17th in groundball to flyball rate among qualified starters. Ordinarily, a pitcher whose ERA jumps around like a House of Pain song is a huge question mark even without Tommy John surgery. But the fact that Nova's 2013 improvement coincided with adding a new, dominant pitch has to be factored into his projections.
Of course, part of his sinker's success should be attributed to hitters' lack of familiarity with it. Even if he completely recovers from Tommy John surgery, those numbers will almost certainly come back down to earth. But the fact that his sinker had the 20th-lowest average vertical movement is very encouraging, especially combined with the fact that only one of the 19 pitchers ahead of him threw the pitch with greater velocity. Keep in mind, a smaller vertical movement value means that his sinker dropped more than most.
Ivan Nova had a ton of forward momentum heading into 2014 which was robbed from him by his elbow injury. But if everything checks out on the medical side, it would not be surprising to see Nova become the front-middle rotation pitcher that the Yankees need him to be. After all, it's not like he is a stranger to the sleeper role.