Castillo begins his first season with the Ducks and eighth season of professional baseball. The outfielder spent parts of three seasons (2014-16) in the Major Leagues with the Boston Red Sox. He combined to play in 99 games, hitting .262 with seven home runs, 35 RBIs, 45 runs, 83 hits, 12 doubles, two triples, seven stolen bases and a .301 on-base percentage. The Cuba native made his MLB debut on September 17, 2014, at Pittsburgh, collecting his first big league hit off Francisco Liriano. His first Major League home run came on September 25 of that season off Tampa Bay Rays pitcher Steve Geltz.

The 34-year-old spent the 2021 season in Japan with the Tohoku Rakuten Golden Eagles. He played in 66 games combined in the Japan Eastern League and Japan Pacific League, hitting .295 with one homer, 17 RBIs, 19 runs, 51 hits, three doubles and a .356 on-base percentage. Previously, the righty hitter was named an MiLB.com Organization All-Star with the Red Sox in 2018. He also earned back-to-back International League Mid-Season and Post-Season All-Star honors in 2017 and 2018 with Triple-A Pawtucket. Castillo was originally signed by the Red Sox as an amateur free agent in 2014.