Diaz has been working on adding a changeup to his arsenal during spring training, Greg Johns of MLB.com reports.
Diaz notched 34 saves this past season but saw his walk rate (11.5 percent) and FIP (4.02) balloon from the year prior. The 23-year-old utilized a two-pitch arsenal -- including a fourseam fastball and slider -- but has reportedly been looking to add an off-speed pitch to his repertoire. General manager Jerry Dipoto recently stated that Diaz's first few bullpen sessions have been "electric" and that his command appears much improved thus far. Lowering his walk rate back into the single-digit range would go a long way towards cementing Diaz as on the the league's preeminent closers.