So far Duffy has done three multiple-inning stints, but there's really no assigned role set for him.
"I'll just come in whenever they ask me to come in. I'll do whatever," Duffy said. "But I'm really enjoying where I'm at right now. I know there's going to be ups and downs, but I feel like I fit really well where I am right now."
Except for closer Greg Holland, nothing is really set. Wade Davis has been the primary eighth-inning setup man, but manager Ned Yost is looking for someone to share that duty as well.
"Once our bullpen gets going, there are really no roles," Yost said. "Anybody can pitch in any situation because they're that good, or they have been in the past."
The left-handed Duffy was a starter throughout his career, but was summoned from Omaha when injuries struck the bullpen.
"The thing that we really like about Duffy is that he's got overpowering stuff. He doesn't have to have pinpoint command because he can get through with his great stuff," Yost said. "You can't constantly be throwing fastballs down the middle, but with his slider, which is new and improved, and his ability to throw an overpowering fastball, we were going to see a lot of innings like we did [Saturday] and the time before."
It appears that Duffy's bullpen tryout might turn into something more permanent this season.
"This is all kind of new to him and we're finding out about how we can use him. Can we use him back-to-back days? We know we can use him in multiple-inning stints. So we're learning about him," Yost said. "I think he's going to be a guy that's going to be very, very durable and be able to throw back-to-back days and handle a big workload down there."
Dick Kaegel is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.