Equinox, believing boxing-inspired group fitness will become the next big thing, just picked up a “significant minority” stake in Rumble, a 12-month-old fitness company with a boxing mentality. Backed by Sylvester Stallone and Justin Bieber — and with a cult following that incudes Selena Gomez, Kendall Jenner, Hailey Baldwin, Jason Derulo, David Beckham and Kevin Hart, Rumble has two Manhattan locations with plans to quickly expand. With such a pedigree, the company was recently valued at about

Read more