Over 26 games, Castillo is batting .230 with one home run, six RBIs and a .544 OPS.
The Red Sox called up the 28-year-old outfielder from Pawtucket on May 22 after 18 minor-league games.
After defecting from Cuba last year, Castillo signed his big contract with the Red Sox and hit .333 (12-for-36) over 10 games in September.
Red Sox manager John Farrell said Castillo was optioned in order to give him regular playing time. Castillo last started a game on June 16 against the Atlanta Braves.
“We just need to get him back playing every ” Farrell told reporters before Tuesday’s game against the Baltimore Orioles. “He had been relegated to a bench role here, which in fairness to him, was difficult to get into any kind of rhythm, gain some confidence in which he needs to with every day play. That is the move with him.”
Also on Tuesday, the Red Sox activated catcher Erik Kratz, who they claimed off waivers on Sunday from the Kansas City Royals, and righthander Justin Masterson. Righthander Steven Wright was also optioned to Pawtucket with Castillo.
The Red Sox entered Tuesday 31–40, last in the AL East.
- Mike Fiammetta