Young pitchers do not grow on trees, especially those that are under 25 years-old. You know this, and I know this. Take a look at 25-and-under pitchers that threw more than 160 innings last season:
That's not a lot! That is less than one of those pitchers per team, and only a handful are definite stars. The rest are either average run-of-the-mill starters, or works in progress.
But even with this knowledge in mind, the expectations for Nathan Eovaldi coming into 2015 were incredibly high. He came off of a 2014 where his ERA and FIP differential was nearly a run (and not in favor of ERA), largely because of his incredibly low walk rate and 6.6 HR/FB%.
That did give him 2.9 fWAR, but that could be a bit misleading. The new pitching statistic from Baseball Prospectus, Deserved Run Average (which adjusts each pitching event for pitch framing, opponent, defense, park, and even temperature), says that his DRA-WARP (WAR based on DRA) was 0.77, good for 206th of all pitchers in baseball. This isn't terribly surprising. Even though he was a FIP darling, you can't be successful as a pitcher when you're in the bottom 20 of Soft Contact%, and in the top 20 of Hard Contact%.
Larry Rothschild is actively trying to sculpt Eovaldi's repertoire, and there will be some growing pains. Here's a look at his repertoire over the course of his career:
Obviously, the first two years of his career were a mess, in terms of consistency. By the time he began starting regularly for the Marlins, he at least figured out that his repertoire would feature his fastball, slider, curveball, and changeup. The thing that has obviously changed, though, is his fastball usage, and the introduction of his splitter in the past year.
Frankly, Eovaldi's fastball has gotten a bad reputation even though it is definitely a decent pitch. By FanGraphs' pitch value metric per 100 pitches (wFB/C), his fastball ranked around that of Zack Wheeler, Edinson Volquez, and Chris Archer. That's not great, and it obviously gets knocked because of the extremely high velocity, but the idea that it is a terribly straight and ineffective pitch does not hold water; even though he does not generate a ton of swings and misses, it does, according to Brooks Baseball, "...result in many more groundballs compared to other pitchers' fourseamers."
But, to make the fastball even more effective, he has been weaning himself off of the higher velocity pitch, resulting in a Fastball% that has gone from 70.6% in 2013 to just 54% so far this season. Why? Well, if Eovaldi wants to maximize the effectiveness of a pitch that is clearly at lightning speed, he needs to mix in off-speed pitches at a rate that sufficiently keeps hitters off balance. That has been evidenced by his Splitter% of 5.95% so far this year, but he just hasn't generated adequate Whiff% (only 22.2% so far, which is well below average for other pitchers' splitters).
And in general, the whiffs haven't been apparent on any pitch. The splitter has definitely shown that it could develop into a decent pitch, and I think that it's incredibly encouraging that he has generated a groundball rate of 88.9%.
We have yet to see Eovaldi's pitch selection stabilize, and I doubt we see that happen any time this year. The fastball usage will likely continue to drop until it is about 50%, and we will get to see larger samples of his curveball and splitter, and whether they can be effective. We don't know if they will be true swing-and-miss pitches--they haven't been at all so far--but they could be pitches that generate a large amount of groundballs for an infield defense that is capable of handling said groundballs. These are the trials and tribulations of your average young pitcher. There will absolutely be ups, and there will definitely be downs (the 0.13 DRA-WARP), but the Yankees have the chance to slowly develop Nathan Eovaldi into a possibly exceptional starter.