Things picked at little in the next 27 games, when his average was .258 (25-for-97) with six doubles, 10 RBIs and, finally, one home run. But a guy who usually hit .300, or close to it, was floundering at .227.
"I knew all along, it wasn't approach. It wasn't my mind," Butler said. "It was something mechanical, and I fixed it."
Well, he and hitting coach Pedro Grifol fixed it, just last Friday and Saturday in fact. And in the last four games, Butler has gone hit .533 (8-for-15) with two doubles, three RBIs and six runs scored. His season average is up to .255.
"Personally, I feel I've made some strides," Butler said. "I'm in the middle of the lineup, a big part of this team and I've got to carry the load a little bit. In big situations, they want me and Hoz [Eric Hosmer] up there. That's why we're in the 3-4 slots, so the more times we succeed, the better off this team's going to be."
If only the flaw in his swing could have been detected earlier.
"You wish you'd see it earlier, but sometimes it's hard to find," Grifol said. "In this case it's something small, but it's a big deal."
It was a relatively simple matter, once Grifol spotted it in his video studies. Butler just wasn't keeping his right elbow tucked in close to his body as he swung, resulting in a lot of harmless ground balls.
Oddly enough, Butler is known as a devoted student of the batting art and of analyzing opposing pitchers, but the issue was something that escaped his notice.
"I didn't feel it when I was hitting," Butler said. "I didn't pick it up until I saw it on video."
Video is a huge part of the work that goes on in the bowels of the stadium, with players and coaches huddled around the screens.
"He made an adjustment in his swing. His back elbow was flying out, which made him come around on the ball, and that's why we we're seeing him hit so many ground balls," manager Ned Yost said.
"He and Pedro went in the cage, went through a lot of video, and Billy being Billy, he can make an adjustment very quick. He saw it and took some swings and felt it. Billy really has an awareness of his body and what he's doing, but he couldn't feel this. He didn't know what was going on and, all of a sudden, he saw it. He made an adjustment and he's back to being Billy now."
The back elbow is kept close to his body now, enabling him to keep behind the ball and drive it.
"It's something where if you keep it away from your body, you come around the ball. There's no way you can stay behind it," Butler said. "It's a term that hitters use -- keeping your elbow in the slot. It's up against your body in the slot, and I was getting out of the slot. And I couldn't feel it."
Not only that, he'd gotten into the habit of letting his elbow fly out, and habits are sometimes tough to break.
"Basically when he doesn't stay in that slot, he becomes top-hand dominant and he starts rolling over balls, and that's where the ground balls come in," Grifol said.
When he keeps that elbow in as he starts his swing, the problem is solved.
"It guides the swing. It creates the path to the ball, and for him, that's huge," Grifol said.
Now, Butler is hitting the ball into the air more often and with more authority.
"That's what we need," Grifol said. "We need Billy to drive some baseballs."
That's just what Butler did in Wednesday night's 3-1 win over the White Sox. In his first time up, he hit a long smash that was caught in right field. For a moment, he thought he had his second home run.
"One hundred percent, I thought it was gone," Butler said. "But you can't control a big yard."
And in the eighth inning, he hit a sizzling sacrifice fly to right field to score the tie-breaking run.
Butler is not really sure how long his elbow flaw was going on, but he immediately went to work to correct it.
"I just had to do some drills to work on it and I'm good now. I still do them every day, and I'll keep doing them the rest of the season, too," Butler said.
Butler broke out with back-to-back three-hit games on Sunday and Monday, victories over the Orioles and the White Sox.
This was more like the Butler who, in the previous five seasons, had hit a cumulative .302 and averaged 91 RBIs and just a hair under 40 doubles and 20 homers per year.
There's a lot of time for Butler to get back to that level.
"You don't judge a player's year for 40 games," Yost said. "You've got to give it the whole year, and if I was a bettin' man, I'd bet Billy's numbers are going to be comparable by the time we get through this year."