At Rumble, a Manhattan fitness studio that could pass for a more hardcore version of SoulCycle, a swanky white entry decked in emoji-like logos and pop art leads to a crimson-lit workout room. Instead of bikes, however, the room is filled with bags, swinging under heavy assault.
Rumble—which launched in New York in 2016 before expanding to Los Angeles and San Francisco, and last year sold a minority stake to luxury mega-gym Equinox—is at the forefront of the boutique-ification of boxing, a sport more likely to evoke the sweaty...