Jonathan Aro

The foibles of Boston's bullpen in 2015 created opportunities for several lesser-known minor leaguers, including Aro, who had three separate stints with the big league club. Apart from his tours in Boston, Aro began the season at Double-A Portland and then pitched mostly at Triple-A Pawtucket, all in a middle-relief role. That's his upside — pitching in the sixth or seventh innings, though he's been used for multiple innings wherever he's pitched. He averaged over two innings per appearance last season in the minors, and Aro was considered for a start late in the season when the Red Sox were scrambling for arms. He throws mostly a four-seam fastball/slider mix — pretty standard fare for a middle reliever — but will add an occasional changeup and sinker. The Red Sox traded Aro to the Mariners in the offseason along with Wade Miley, and Aro will presumably get a chance to compete for a front-end job in spring training.