What are the criteria for a player to have his number retired by the Arizona Diamondbacks?

The D-backs currently have two retired numbers in addition to Jackie Robinson's No. 42, which is retired throughout baseball.

Outfielder Luis Gonzalez was the first former D-backs player to have his number (20) retired, in 2010, and he was followed in '15 by Randy Johnson, whose No. 51 was retired following his enshrinement in the Hall of Fame that same year.

"One is the greatest pitcher in our history and the other is arguably the best offensive player in our history," D-backs team president/CEO Derrick Hall said. "And they're the most popular players that we've ever had wear the uniform."

Former D-backs right-hander Curt Schilling has a good chance of being inducted to the Hall of Fame next summer, but he is unlikely to choose to have a D-backs hat on his plaque, which puts him into a gray area.

Schilling had a relatively short tenure with the club, joining them on July 26, 2000, and departing following the '03 season. While the right-hander won a World Series in Arizona, he spent nine years with the Phillies and he won two World Series with the Red Sox.

"We would have a decision to make," Hall said. "He's talked about going in without a team because of his long history with the Phillies and his success here, but who knows?"

Outside of a player like Johnson, who chose a D-backs hat for his Hall of Fame plaque, there is no specific policy, yet.

"Right now is really the perfect time to adopt one," Hall said. "Obviously we hope there's going to be more Diamondbacks in the future in the Hall of Fame. But let's say there never are. You still want the ability to retire a uniform number of someone who has had a tremendous impact on your franchise and your community."