How exactly his time will be spent is still up for discussion.
"I don't know clearly yet what my responsibilities will be yet, I think as time goes on I'll be where I'm needed and try to do whatever I can to try and improve the quality of pitching in the Diamondbacks organization," Duncan said. "If somebody has questions or wants to talk baseball, I'll be there to talk it with them. I think I'll try to express my philosophies about how I think what philosophy you have to have to be successful as a pitching staff. And hope that I can contribute however needed."
During his time as pitching coach for the White Sox (1983-86), A's (1986-95) and Cardinals (1996-2011), Duncan was regarded as the gold standard, with four of his pitchers winning Cy Young Awards.
Duncan had been out of baseball since the end of the 2011 season. He had taken a seven-week leave of absence that year to be with his wife, Jeanine, who was fighting brain cancer.
With manager Tony La Russa retiring as manager of the Cardinals and Jeanine still battling cancer, Duncan remained out of baseball in 2012 and '13. Jeanine passed away this past June.
"I really haven't had time to miss the game," Duncan said. "I spent the last two years caring for my wife. The last year it became more intense. I still followed the game, I read the papers and I watched games on TV, but miss it? No, I didn't miss it. That was a low priority for me at that particular time."
After Jeanine's passing, though, Duncan realized that he had isolated himself too much.
"I thought for many reasons -- mentally, physically, everything else -- I needed to be doing something," Duncan said. "Since my wife passed away, I have been pretty much a hermit and I knew that was not a healthy to do. And I felt like if I could get back in the game in some capacity, not full-time, I thought that would be in my best interests."
The D-backs had initially hoped to hire Duncan to replace pitching coach Charles Nagy, who was dismissed after three seasons, but Duncan was unsure he could commit the time and energy that the position demands.
"In order to do the job right it's very time consuming, it's very stressful, you've got to really putting everything you've got into it 24 hours a day during the season and during Spring Training," Duncan said. "I just didn't feel like I was ready to make that kind of a commitment again right now. I don't know how I'll feel a year from now, two years from now, but right now, I just didn't feel like I could make that kind of commitment."
Duncan picked the D-backs over a lot of teams that expressed interest in having him join their organization.
"I chose the Diamondbacks because I have a son that lives in Tucson [with] two grandkids, and my other son lives in Laguna Beach, which is not far away. So it put me in a location where I can be more accessible to them," Duncan said.
Duncan is playing a role in deciding who the next pitching coach will be, having sat in on recent interviews. D-backs GM Kevin Towers said that Duncan's presence in those interviews has been a "huge help."
In addition, Duncan has received a crash course from Towers and manager Kirk Gibson on the organization's pitchers.
Over the next few months, he plans to do even more studying to make sure he has a feel for the pitchers come Spring Training.