The decision follows a two-error, two-strikeout, 0-for-4 game for Castellanos in Tuesday's 6-2 loss to the Astros. Castellanos' remarks after the game sounded like he knew this was coming.
"I don't believe in [fatigue]," Castellanos said Tuesday night. "I want to play more. The past is what it is, and the only thing I can control is how I look toward the future. It's up to Brad, but he knows every day, I want to be in there."
Castellanos had started each of the Tigers' first 44 games this season. Ausmus exercised patience with him, trying to give him a chance to ride out a cold start that saw Castellanos make plenty of hard contact with pitches but get little offensively to show for it.
Tuesday's 0-for-4 dropped Castellanos' average to .220 and his OPS to .677, 150 points below his rate last year. The 25-year-old has 10 doubles, three triples and four home runs, but with 53 strikeouts, he has struggled to take advantage of batting second in front of Miguel Cabrera in Detroit's batting order.
"There's no question that if you are not getting results, you want to fix it, [even] when there's no fix to be needed," Ausmus said. "You feel like you have to do more."
The Tigers did not take batting practice Wednesday. Castellanos spent part of the pregame in the dugout talking with defensive coordinator Matt Martin. Andrew Romine started at third place in place of Castellanos.
If this approach sounds familiar, it's the same reasoning that Ausmus and the Tigers used last year in holding Upton out of the starting lineup for three games in mid-August. Upton was batting .226 with a .653 OPS at the time. He hit .309 with a 1.162 OPS over his final 38 games once he returned to the lineup.
"Actually, we did it with Nick a few years ago," Ausmus said. "It's more reset mentally than anything else, wipe the slate clean."
The other factor with Castellanos this time is defense. His nine errors on the season match his total from last year, though his defensive metrics haven't been quite as bad. He has worked on a throw off his back foot that has helped him convert ground balls down the line into outs.
Even so, Ausmus said he has to be more consistent with his defense.
"There have been a couple lapses, this road trip and prior to last road trip," Ausmus said. "I think maybe it's a reminder of how difficult it is to be a good defender, and how you still have to continue to put the work in, not just go through the motions. It has to be real work.
"Maybe the struggles with the hitting played into it. But ultimately, we need him to play. We need him to hit and play defense, so hopefully a couple days can help him get back there. Because he looked really good in Spring Training, I thought, and the beginning of the season. So we know it's in him. We know it's there."