I'm from Tulsa, but have lived in the ATL for 10 years now, and I've never really experienced anything like this grassroots fandom that has been built over the last couple of years. It's a different type of energy and a different type of fan. These aren't your typical fans of the Falcons and Braves, although there is some overlap. It is a diverse fanbase that is rabid. When the announcers say that every fan stands for the full 90 minutes, they aren't kidding. It is raucous.
I've only been to one match so far, but it was by far the most electric sports environment I have ever seen.