Olivia Rodrigo may be a teenage pop star who works for Disney and first scaled the Hot 100 with a piano-driven ballad, but her second No. 1 of 2021, “Good 4 U,” is a surprisingly feisty pop-punk song. And Sour’s even harder-rocking opener “Brutal” is currently ascending Billboard’s Alternative Airplay chart. Rock music has been deeply intertwined with American pop ever since early rockers like Little Richard and Bill Haley started scaling the charts. But since the ‘80s, Top 40 radio has largely favored sleeker tracks with synthesizers, drum machines, and influences from genres like dance music, R&B, and hip-hop, with only occasional bursts of electric guitar and live drums. Plenty of rockers have become pop stars, from Pat Benatar to Bruce Springsteen, but there are also pop stars who ...