The Cardinals are playing all 9 AAA players tonight, Bailey will not give up much. Shelby Miller is a killer and should be a strong 1 or 2 in a year or so, I don't think Cinci will put up too many especially because there isnt much film on him. Add in a cool night with no wind in STL, the 7.5 is generous.
Edit: Cinci also isnt playing for anything, I dont think their starters will end the game.