Fans of BROCKHAMPTON were getting antsy. It had been 45 minutes since the show’s scheduled start time Saturday night, and there was still no sign of the band. Any glimmer of action earned an exaggerated reaction from the audience. An audio recording of Agganis Arena safety protocol set off roaring cheers.

To hear frontman Kevin Abstract call his collective “America’s favorite boy band” is deceptive — but so is Brockhampton. Although they are often compared to the Los Angeles rap group Odd...