The problem is, only a few people not associated with a team are allowed to buy rings unless they are sold at auction later by collectors. Rudy got four.
And Rudy was also instrumental in getting all kinds of taxpayer-funded support for the new Yankee Stadium being built.
So it certainly gives the appearance of impropriety. Especially if arrangements were made by the team and Rudy to buy the rings at a later time while Rudy was still mayor.