To come up with the rankings, professor Michael Lewis at Emory University used three key criteria: Fan equity, social media equity and road equity. In a nutshell, the Fan Equity criteria basically revolves around how much fans are willing to spend on their team and how much support they show with their wallet.
Social media equity is exactly what it sounds like and ranked fans by how many social media followers that each team has. The third criteria, road equity, is based on how much support each team gets on the road.