After losing Rafael Soriano, Mariano Rivera, Joba Chamberlain, and Boone Logan over the last two seasons, the Yankees have made one Major League free agent addition to their bullpen, Matt Thornton. Thornton won't be replacing Rivera, but he'll step in as a greater-LOOGY to a Yankee team that just lost Boone Logan to the Rockies.
Thornton spent most of his career with the White Sox where he was a highly successful left-handed setup man. Unlike most left-handed reliever, Thornton throws in the mid-90's and his stuff was once good enough to retire left-handed and right-handed hitters alike. Since 2010, his fastball velocity has declined from 96.1 mph on his four-seam to 94.3 mph in 2013. This velocity drop has correlated with his efficiency, as his strikeout rates have continued to drop from 12.02 K/9 in 2010, to 9.50 K/9 in 2011, to 7.34 K/9 in 2012, and finally 6.23 K/9 in 2013. His ERA has subsequently increased, but not all that substantially. While the difference between his 2010 2.67 ERA and his 2013 3.74 ERA is significant, Thornton has gotten there with incremental steps every year. There was never a major dropoff in his stuff or his results, which points to possible age regression.
Thornton has made a career as a hard throwing left-handed pitcher that earns strikeouts, but that is not why he was mildly successful in 2013. Somewhere over the last four years, Thornton has adopted into a contact pitcher with a sinker, and over the last three seasons he's earned just over a 50% ground balls. This limits extra base hits, and despite playing in hitter-parks like U.S. Cellular Field and Fenway Park, he's used this ground attack to limit home runs from right-handed hitters.
In his age 37 season in 2014, Thornton will could take another step back against right-handed hitters. In 2013, he struggled much more than usual, allowing a .370 wOBA to righties compared to his career .299 wOBA. Oddly enough, Thornton wasn't hit hard by right-handed hitters, allowing just 4 extra base hits, but he was hit more often and did give up a number of walks. There's certainly rebound potential versus righties, as his failures in 2013 seem to be a matter of small sample size rather than diminished stuff. Still, the Yankees plan to put Thornton in the Logan-type relief roll, which will limit his appearances versus righties.
Yankee Stadium should also give Thornton a slight benefit compared to the previous two ballparks he played in. Right-handed hitters typically tee off in Chicago and Boston, and although it's no easy park to pitch in, Yankee Stadium is technically harder for right-handed hitters looking to pull the ball. With that said, Thornton's groundball heavy approach could be an issue with the current infield. Kelly Johnson is somewhat of a mystery at third base, Derek Jeter should not be a good fielding shortstop, and Brian Roberts and Mark Teixeira offer good defense but may have issues staying on the field.
Despite the declining FIP, I do think Thornton will improve on his 2013 4.04 FIP this season. I think he's capable of a 3.75 FIP, and he may overperform that just slightly with a 3.60 ERA. Hopefully Larry Rothschild can find a way to get his strikeouts to return, in which case Thornton could re-emerge as a high-leverage pitcher. For the moment, I'm looking forward to Thornton as an upgrade over Boone Logan.