DETROIT, Oct. 30 -- The Mumford & Sons frontman watched his first NFL game on the Ford Field sideline, greeted Jared Goff, then played a sold-out arena set as Detroit won.

Marcus Mumford walked onto the sideline at Ford Field a little before kickoff and did what any first-timer does in this stadium. He craned his neck to take in the tiers, he studied the sightlines, he let the noise crawl up his shoulders. It was his first NFL game, and the lead singer of Mumford & Sons had timed it like a stage cue, a quick cameo in Honolulu blue before a sold-out show a short walk away at Little Caesars Arena. The overlap was not an accident. It was a favor to a friend, and a nod to a city that fills two buildings on a Monday night.

The friend is Jare...