Having pitched four of the last five days, Casilla wasn't available for Wednesday's game, Bochy said.
After Casilla gave up two hits in the ninth inning of Sunday's game, Bochy visited the mound to check on his closer, whom he had pulled in the ninth inning the previous game. After staying in the game, Casilla threw six straight fastballs to Norris after starting the at-bat with a curveball in the dirt.
"I went out there myself to look at him in the eye and talk to him a little bit," Bochy said. "I liked his answer and he came back and struck out the next guy on three pitches. On the next series, he went to the well one too many times. In the moment, he looked like he just reached back and let it go instead of methodically thinking of where to put the ball. He was just going to bull his way through."
In the Giants' 9-8 win against the A's on Saturday, Bochy pulled Casilla after he gave up a run on two hits and a walk, leaving the game without registering an out.
"In the game I pulled him, I watched him throw the secondary pitches and he was overthrowing," Bochy said. "He couldn't get them over, and in my mind, he was off. I think part of it was Oakland, being a little hyped up, but he wasn't even close on a couple breaking balls."
Bochy said Casilla understood being pulled, but the skipper is still conscious of supporting the team's closer.
"I have to do what I think is best for the club," Bochy said. "Sure, you're sensitive to that, and you want him to have confidence in him. The times I have pulled him, I bring him in and tell him and say, 'Things weren't right, I made the call.' It's important that they know that they're the guy and you're behind him."
Bochy said Casilla doesn't have the leeway of predecessor Brian Wilson, whom Casilla replaced after the three-time All-Star closer's Tommy John surgery in April.
"A lot of things are earned in this game, and Wilson, sure he kept you on the edge of your seat, but he found a way to get it done," Bochy said.