Boxing and (especially) American football have long histories and devoted fans, but there’s more and more unease as awareness grows of the brain damage athletes in those sports can sustain. Since gymnastics became popular in the 1970s, “we know more … the sport’s history of sexual and emotional abuse, its amplifications of adolescent body-image problems, and its complicated coach-gymnast relationships. The sport’s obsessive focus on the body and self-presentation is like kerosene poured on the flame of female adolescent self-scrutiny.”