The play resulted in a pair of Cardinals runs and left the Cubs shortstop on the ground for a prolonged period of time.
Castro was among many in the Cubs' postgame locker room who was unhappy with Holliday's approach.
"I was hurt on the ground and didn't think too much about the runs," Castro said. "He was really out of the base [path]. He didn't have a chance to touch the base. He slid hard, real hard. It wasn't clean."
Potentially, if Holliday was called out on an illegal slide out of the baseline, the Cubs would have walked off the field with a 5-3 lead. Instead, St. Louis put up eight runs in the inning to knock out starter Rodrigo Lopez and reliever Jeff Samardzija in the process.
Manager Mike Quade argued with second-base umpire Daryl Cousins until he was ejected. Quade's primary objection was that the intent of Holliday's slide was to take Castro out rather than reach second base.
"I applaud somebody who will go in hard to try and break up a double play," Quade said. "But my thing is, it's not a legal slide to me. The way Starlin was clipped, in retrospect, the bag was the last thing on his mind. They don't [call an out] unless it's blatant. The rules are there for a reason."
Castro said he was fortunate to avoid an injury.
"It's only OK because he had a rubber cleat," Castro said. "If he had a [steel cleat], he would have cut me."
The Cardinals scored 13 unanswered runs after the Cubs plated five in the first. Marlon Byrd's ninth inning double was the Cubs' only hit after the first inning.
"Momentum in the game is huge," Quade said. "You get a 5-3 lead, but as that inning progresses you really lose momentum.
Bruce Levine covers the Cubs for ESPNChicago.com.