The pregame scene outside Baltimore’s M&T Bank Stadium on Saturday likely felt familiar to anybody who has followed Lionel Messi’s time in Major League Soccer. Fans milled about, forming a colorful patchwork of Inter Miami pink, the light blue and white of Argentina’s national team, and in this case, the purple of the NFL’s Baltimore Ravens. Others simply came in whatever soccer jersey they happened to own, all the way down to indoor soccer’s Baltimore Blast, the closest thing the city normally gets to top-flight soccer.

What there wasn’t a lot of was DC United black and red. Despite its proximity to the nation’s capital, Baltimore isn’t exactly DC United country, and as far as decision-makers at United are concerned, that was an opportunity. The club moved the Miami match away from their usual home, the 20,000-capacity Audi Field, to maximize ticket sales, but also to put themselves on display to potential fans in Charm City, a market they’ve badly wanted to engage for years. DC are in the process of starting an MLS Next Pro team in the city, and they’ve partnered with Baltimore’s local government to construct a stadium here for that club.

The relocation mirrors...