The Yankees have a ton of players to help contribute to the bullpen this season, but losing Mariano Rivera has made the entire system seem much less appealing. No one can replace the closer, but David Robertson projects to be a strong one. The 8th inning is an even bigger downgrade, as the organization has no idea who will take over Robertson's setup role. Shawn Kelley, Adam Warren, Preston Claiborne, David Phelps, and Dellin Betances are all candidates for that setup job.
Going off of last year's performances, Kelley probably has the best chance of becoming the 8th inning guy. In 2013, Kelley put up an incredible 11.98 K/9 with a 3.88 BB/9. Unfortunately, the fly ball heavy pitcher gave up a ton of home runs, 2 at home and 6 on the road. Kelley finished the year with just a 4.39 ERA, but the numbers look a lot different when you consider he pitched through the last month of the season with a tricep strain. If you take away his numbers from September, Kelley posted a much more respectable 3.60 ERA.
The reliever also had a rough early start to the season, posting an 8.71 ERA in his first 9 games. Half of his 8 home runs came in the first five appearances of the season. According to PITCHf/x, not only did Kelley average about a mile less on his pitches in those first few games, but his movement was dramatically weaker. By mid-season, Kelley had a fastball with more than a mph more velocity, more than an inch more movement into right-handed batters, and more than an inch more of vertical rise. His slider had nearly 2 more mph, and it was much tighter with a decrease in movement towards left-handed batters, and much less of a vertical drop.
The improvements that Kelley made were likely due to strength, as many pitchers show similar improvement as the season goes on. The huge difference between good Kelley and bad Kelley does not seem to deviate from appearance to appearance, rather it happened in 2013 based on his physical ability in April and September. If he wins the setup role in 2014, we can assume that good Kelley showed up with the same strength he had by mid-season in 2013.
Now that he's been thrown into a competition where he can be a high-leverage reliever, I expect him to do as much as he can to win that job. The 2.27 ERA that Kelley owned through 42 mid-season games is a little bit lofty of an expectation, but the talent is undoubtedly there, and his success as a fly ball and strikeout pitcher will help him earn high-leverage opportunities. Home runs will always be a factor to worry about, but it's a necessary evil that may be overcome by his brutal slider.
With very little difference in splits and a perfect high-leverage type approach (K's and fly balls), Kelley has some of the highest potential as a setup man. If he can put it all together, avoiding injury and a slow start, Kelley has shown he can be as good as Robertson. There's also plenty to question about Kelley though, but with the depth the team has added, it seems that Joe Girardi will manage to find someone capable of handling the 8th inning. If Kelley is that guy, I'd put him at a 3.30 ERA with a 3.60 FIP. Fortunately, the improved outfield defense should help him outperform his FIP thanks to his fly ball tendencies. Expect his strikeouts to maintain, and after posting his second highest BB/9, I think his control may rebound as well.