Despite the fact that it ended in heartbreak when Terry Collins left him in an inning too long in the World Series, Matt Harvey had an excellent 2015. Overcoming the usual problems associated with Tommy John surgery and a hotly-debated innings limit controversy, Harvey had a 2.71 ERA over 189.1 innings, tacked on another 26.2 innings of 3.04 ERA ball in the postseason, and ultimately silenced any critics who accused him of abandoning his teammates.
While 2015 was a remarkably effective return from Tommy John surgery, Harvey was nowhere near his pre-surgery form. He posted the 17th-highest fWAR among starting pitchers (4.4) in 2015, but that represented a big step back from 2013, when he posted 6.5 WAR in only 178.1 innings, a higher WAR/IP than Clayton Kershaw. More granularly, Harvey's strikeout rate dropped by nearly a full batter per nine innings, and his home run rate more than doubled. His ERA was half a run higher and his FIP increased by 1.05.
Per his own comments, Harvey's slider was greatly limited for the first half of 2015, and his results struggled without the pitch that made him such a force in 2013. After a start in July against the Dodgers, Harvey commented that he'd made some adjustments and had the pitch back. Over the remainder of the season, the spin rate (per Statcast) on his slider increased as did the number of whiffs, going from 17% to 20%. Harvey's bottom line results also improved, as his ERA dropped from 3.04 before that start to 2.15 after it.
Lacking his best pitch did have some benefits for Harvey, as it forced him to use and improve the rest of his arsenal. Most notably, the whiff rate on his curveball improved from 12.8 percent in 2013 to 16.4 percent last season. Placing that improved pitch aside Harvey's devastating slider—which he mentioned feels good and has better spin after his first spring training start—should allow Harvey to improve on last years results and perhaps allow him to achieve his 2013 level of production once again.
Projecting any pitcher whose name doesn't rhyme with Bershaw to perform like Harvey did in 2013 is disingenuous, but Harvey has the potential to shatter every reasonable performance estimate in 2016, especially if he has his elite slider back. Even if he only performs like a top-15 pitcher instead of a top-3 one, a Dark Knight with a fully restored utility belt should strike fear into any batters that wander into Gotham.