The reason? Duffy couldn't command his two-seam fastball, and a balk call in the second inning took away his slide step for the rest of the game, he said.
Duffy railed on the call, which came with runners on first and second and two out and Omar Narvaez at the plate. On a 1-1 pitch, home-plate umpire Bruce Dreckman called a balk, indicating to Duffy that he didn't reach a full stop in his set.
Royals manager Ned Yost said after viewing the replay, Duffy indeed came to a stop. Duffy agreed, vehemently.
"It was garbage," Duffy said. "It was terrible. A terrible call. You have to be legitimately looking for that to make that call. That takes away my biggest weapon, which is my slide step. It's something I've been working on for 10 years. I wasn't happy with it.
"It's not sour grapes. I still need to locate and make pitches, but that was a terrible call. In that situation, you just have to let the players play, man. There's an umpire right behind the mound who can make that call if he needs to, but he didn't feel the need to make it. And I was leery to make that slide step the rest of the game.
"I'm sure [Dreckman] was trying to make the right call and I'm sure he's a good guy, and he's trying to do his best. But it took away one of my best weapons. He said I didn't stop and I did stop. One-hundred percent. But I'm not one to make excuses and I need to make pitches. That call didn't get into my head, but it took away my biggest weapon -- I slide step about 60 percent of my pitches."
Duffy only allowed one run that inning on Leury Garcia's single. But from the time the balk was called until Duffy left the game, he began exaggerating his stops in his sets, to make a point.
"Whether I get repercussions for what I'm saying right now ... he took away one of my biggest weapons," Duffy said, "and I was worried about it the rest of the game."
Duffy also had command issues, especially with his two-seam fastball. Duffy had thrown the two-seamer 30 percent of the time this season, his most-used pitch. On Tuesday, he threw just 18 two-seamers of 96 pitches.
"I still have to command my pitches," Duffy said. "I still have to locate. ... I'll be fine next time out."