I had to do some research, but depending on your parameters, it might be Providence, Rhode Island. If you're including places like Brooklyn, Staten Island and Newark in the greater New York Metropolitan Area, and Boston=New England and such.
I'm including places in the same area if a team was placed in city X to replace a team from city Y, with the intent to reach the same fan base. The Patriots moved around a bunch but they never were leaving their fanbase to move to a new city. When the Texans and Browns returned, they were replacing lost teams from Houston and Cleveland. I'd consider the Jets and Giants moving to Newark as similar to what the Pats did, but I'd say Brooklyn and Staten Island "lost" teams that weren't replaced. But that's just me.
90% of the football fans in Brooklyn and Staten Island are fans of either the Giants or Jets, so I don't see how you can consider them serving a different fan base than those who rooted for the Brooklyn Dodgers or the Staten Island Stapletons. Heck, they're officially part of New York City anyway.