"He couldn't get loose throwing this morning," said Red Sox manager John Farrell. "After the dive in the eighth inning, he jarred the right shoulder, so he's out today. He felt like he could swing the bat, and that was even the case last night if his at-bat came up in that final at-bat.
"But he was not going to go on the field defensively if we extended that game. He tested out the same this morning. There's a couple of plains in the physical testing where we were able to reproduce the discomfort. We think this is minor in nature, but he didn't feel comfortable trying to get loose here this morning."
Castillo continues to be a victim of nagging injuries. Earlier this season for Triple-A Pawtucket, he jarred his left shoulder on a similar play.
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.