The Cubs' 21-year-old shortstop failed to catch a popup in the first inning on Wednesday, and manager Mike Quade spoke to Castro and second baseman Darwin Barney about the importance of defense after the game.
"I didn't see the ball," Castro said Friday. "The ball went up, and I called it, but when the ball came back, I lost it."
The ball, hit by the Phillies' Michael Martinez, dropped next to Castro, and Martinez eventually scored. Cubs pitcher Ryan Dempster gave up two runs in the first, and lasted three innings in the loss.
Did Castro feel he did anything wrong on that play?
"Losing the ball, that's it," Castro said. "I saw the ball when it came off the bat and I said, 'I got it.' When the ball came down, I lost it in the sun."
And next time?
"Don't say 'I got it,'" Castro said. "If you don't have it, don't say, 'I got it.' Say, 'I don't see it.'
"That kind of thing happens," he said. "Next time, my teammates can help me."
Quade said he expected better communication between the middle infielders.
"I'll bet these two have it worked out the next time it happens," Quade said. "The premium that goes on defense at those two positions is the main thing. They'll work it out and they'll get better, and they need to.
"Instinctively, with those two kids being together, the minute the ball goes up here at home, you need an understanding of what may or may not take place," Quade said. "It's another learning experience for those guys. I really believe they'll be here together for a long time, and don't want to see a mistake like that happen again and don't believe it will."