With the plan the Red Sox have outlined, Castillo will get to 200 total plate appearances before starting his offseason. Those plate appearances include the ones he had at Boston's Minor League affiliates, and the ones he will get for the Red Sox before the season ends on Sept. 28.
"I would think, by the time 200 at-bats rolls around, you're looking at maybe mid-November I would guess as a rough estimate calendar-wise," said Red Sox manager John Farrell.
Castillo is getting the extra at-bats to make up for the fact he didn't play any baseball for a 13-month span before signing with the Red Sox.
Friday night marked Castillo's second start in the Majors. He went 1-for-4 in his debut on Wednesday.
Ian Browne is a reporter for MLB.com. Read his blog, Brownie Points, and follow him on Twitter @IanMBrowne. This story was not subject to the approval of Major League Baseball or its clubs.