Kaplan's math is regarding applicable amusement taxes is a little messed up. He correctly notes that patrons currently pay 12% amusement tax on tickets for games at Wrigley. That 12% tax = 9% Chicago amusement tax + 3% County amusement tax. So far, so good.
But Kaplan goes on to say that there would only be a 3% amusement tax for games at Rosemont. That is wrong. For Rosemont games, there would be a 3% Rosemont amusement tax + 3% County amusement tax = total of 6% amusement tax. And, yes, there is case law supporting this. See County of Cook v. Village of Rosemont
, 303 Ill. App. 3d 403 (1st Dist. 1999).