"MLB called and said it was a violation of the taxi-squad [rule]," manager Ned Yost said.
"This is where common sense needs to come into play. A violation of the taxi-squad rule is if you've got a player hanging here that's available -- you've got a guy here three or four days in case something happens, that's a clear violation. This kid's not available, but they said it's a violation of the taxi squad -- get him back."
Duffy worked six innings, held the Tigers to one hit and outpitched Justin Verlander in the Royals' 2-1 first-game victory.
"He was going to fly back [to Kansas City] with us," Yost said. "My thinking is, 'OK, the kid pitched his butt off, he's unavailable, let him stay here, throw a side session, he can fly back with us and go to Omaha.' A little bit of a reward."
But no. Duffy was off to Memphis, where he'll sit on the Storm Chasers' bench. He's scheduled to pitch for them on Wednesday, after they return to Omaha.
Dick Kaegel is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.