On a sunny Saturday in Atlanta, a day before the Carolina Panthers’ Week 2 matchup against the Atlanta Falcons in 2018, Diesel Filling Station, an old former pump station on Highland Avenue that is now a bar (with the best lemon pepper wings in town), was packed.



College football was on in the main room — Auburn versus LSU.



A small television up near the bar, however, was playing that afternoon’s Atlanta United game against the Rapids in Colorado. While a raucous crowd of orange-clad Auburn fans near the door celebrated (and then mourned a loss to the other Tigers), an equally-loud group of soccer fans in red Atlanta United gear was glued to the smaller set, energetically cheering for their city’s very own young, but wildly successful soccer team. The next day, thousands of Atlanta Falcons fans would pour into Mercedez-Benz Stadium downtown — where Atlanta United also plays — to watch the Falcons take on the Panthers.



That...