LOS ANGELES — Nicholas Hoult laced up his black Adidas sneakers, grabbed an orange jump rope and found a spot in the alleyway behind Trinity Boxing Club, a no-frills gym behind Melrose Boulevard in Los Angeles.

It was an early Wednesday morning, and the light was still soft. As the rope whistled under and over him in one seamless motion, Mr. Hoult appeared to hover in the air like a gorgeous human hummingbird.

“Beautiful,” said Eddie Arrazola, his trainer. “I train a lot of actors, and a lot of them don’t pick it up, but Nick actually knows how to box.” Mr. Hoult batted off the compliment with a shake of his head.

After the 10-minute warm-up, Mr. Hoult bounced inside the boxing club, which smelled like old leather and stale sweat. The gym resembled a set from a movie, its black walls plastered in rah-rah quotes from great men of history handwritten on canvas panels.