My friends and I are coming to the double header on the 28th. Would we need a parking pass for both games? Also do we need a ticket for the concert that's afterwards?

If you need transportation to and from your car Cobb county has a shuttle that runs around the stadium until 2:00am it's called the blue and green circulater and it is free

Concert is included with ticket purchase.

One parking pass will be enough. I'm not sure about the concert, though.

I would call the stadium just to be sure.

Concerts afterwards are usually free with admission.

You should call the stadium and ask