Where is the con?
I love Diggstown. Seen it at least 20 times. But I've never understood why it's considered a confidence-game movie. The first time we meet Honey Roy, working with the kids at the Y, he says to Gabe, "I'm off the con." The UK title for the film is "Midnight Sting," obviously aiming for the crowd that loved The Sting, which involved a genuine confidence game. In The Sting, Gondorff and Hooker, and their crew, weren't relying on a genuine horse race. Every last thing was fixed.
In Diggstown, other than a few shortcuts that Gabe arranges to lessen the challenge of Honey Roy fighting ten men in 24 hours, there is no real con game. He lies about Fitz in order to seduce the mayor of Diggstown into the bet, but Honey Roy still has to fight 7 out of 10 bouts legitimately -- any one of which he could have lost, save for his skill as a fighter. In a con-game movie, you don't usually see the outcome hanging on such a legitimate show of talent.