Nikki Jennings started cheering when she was 4 years old. She was small and flexible and became a flyer, a human baton spinning and twisting through the air before being caught by teammates. Until sometimes she wasn’t: She got her first concussion in the third grade.
Jennings was a budding star, and at 13 she joined a competitive gym called Rockstar Cheer in Naples, Fla. She was the golden child of her coach, Carlos Realpe — even if he sometimes pushed her too hard. Like when he ran practices late into the evening on school nights. Or when Jennings pulled a hamstring and he threatened her position on the team unless she pounded ibuprofen and powered through the pain. Or when he screamed and threw shoes and water bottles. (Realpe denies throwing things; two other team members supported Jennings’s account.) Parents of other children complained about Realpe’s coaching style, but Jennings brushed it off…