Before playing the most high-profile concert of his career, Josh Meloy had a routine to keep.

Outside his dressing room, the backstage halls at the Criterion, a mid-sized rock room in downtown Oklahoma City and benchmark for up-and-coming bands passing through, were nearly as crowded as the sold-out venue itself. This was in early February, and Meloy was headlining the 3,300-capacity room for the first time, with parents, wives, children, aunts, uncles, cousins — anybody considered family to Meloy and his five-piece band — all welcome. It created the type of chaos...