The Yankees traded away a very underrated player in Francisco Cervelli in order to land lefty reliever Justin Wilson. Wilson was dominant in 2013, pitching to a 2.08 ERA in 73 2/3 innings. In 2014, he regressed significantly, putting up a 4.20 ERA in 60 innings. The Yankees have stated that they think his true ability is comparable to former Yankee Boone Logan, who put up a 3.38 ERA over four seasons in pinstripes. But Wilson's extreme velocity provides hope for a higher ceiling.
Comparing Wilson to a mid-3's ERA lefty reliever isn't unfair by any means. His FIP over the past two seasons was 3.50. FIP, which attempts to adjust for BABIP, is generally considered to be a better measure of a pitcher's true ability. Hitters' BABIP against Wilson went from a crazy low .229 in 2013 to .285 in 2014, still below league average, but understandable given his ability to get groundballs. Wilson also struck out and walked more batters in 2014.
The biggest difference between the past two seasons was his sinker. In 2013, opponents hit .161 against his sinker and slugged just .179. However, the pitch went from exceptionally good to terrible overnight, as hitters put up a .362 BAA and a .447 SLG in 2014. Hitters simply had no trouble squaring up Wilson's sinker with a massive 30% line drive rate and a tiny 7% whiff rate. By the end of the season, he had effectively phased the sinker out of his arsenal:
What actually happened to his sinker is unclear. Fortunately, he might not even need it going forward. The Yankees were initially interested in Wilson because of his premium velocity. In 2014, his fastball averaged 96.3 mph. According to Baseball Prospectus's Pitch F/X leaderboard, only three left-handed pitchers threw harder. As it turns out, Wilson's four seam fastball is pretty comparable to some of the other notable lefty fireballers:
|Pitcher||Avg. Velocity||Avg. Vertical Movement|
|Jake McGee||97.45 mph||11.06 in.|
|Sean Doolittle||95.32 mph||11.79 in.|
|Justin Wilson||96.31 mph||11.31 in.|
Unlike Wilson, both McGee and Doolittle threw their fastball rougly 90% of the time. Also, at 11 inches of vertical movement, all three pitchers have "rising" fastballs. Of course, their fastballs don't actually defy gravity, they just fool the hitter by not dropping as much (nine inches of vertical movement is the league average). A recent post from FanGraphs' Jeff Sullivan indicates that rising fastballs are most effective when thrown higher, something Wilson has not done as much as Sean Doolittle, according to Brooks Baseball's heatmaps:
The best course of action might be simply emulating Doolittle's strategy of throwing mostly elevated fastballs. Oakland's All Star closer pounded the strike zone, allowing just north of one walk per nine innings. He basically said, "Here's my fastball, hit it if you can." Even though hitters knew there was a 90% chance a fastball was coming, Doolittle was able to pitch to a 2.73 ERA and a 1.71 FIP. If hitters have significant trouble with Wilson's fastball, which they should, he might not even have to worry about his sinker going from elite to awful last season.
More importantly, bounce-back seasons from both Wilson and David Carpenter would quite possibly give the Yankees the first ever four-headed bullpen monster. After all, having a shaky rotation matters a lot less when the other team effectively has five innings to score.