Gender and masulinity is are at the center of Billy's problems, even though he sees no issue with his interest in ballet. In the town where he is from, boxing is for boys and ballet for girls, yet Billy's deep love for dance draws him towards ballet nonetheless. At first, he himself is confused about whether his interest in ballet belies some kind of effeminacy, but soon learns that male ballet dancers are some of the most athletic men in the world, which reassures him.
Even though it doesn't take Billy long to learn that ballet doesn't make him less of a man, it takes his brother and father awhile longer to catch up to him. They are convinced that ballet is for women and gay men, and their bigoted attitudes prevent them from seeing Billy's immense talent. Their perceptions of gender prevent them from accepting what is right before their eyes.
Additionally, Billy's best friend Michael is coming to terms with being gay, experimenting with cross-dressing and his own effeminacy. While Billy's discipline of choice, ballet, marks him as subverting gender / masculine expectations, Michael grapples with the fact that he isn't like other boys in key ways. Billy, an ever-sympathetic protagonist, accepts Michael and encourages his friend's effeminacy, bringing him up to the gymnasium after hours and putting him in a tutu.