OCs are talented in a type of sport, but being the gender they are, they're not allowed to participate. Eventually, OCs cross dress and begin participating, quickly becoming one of the best people in their sport. Eventually, OCs fall in love with another competitor/team mate and this person begins questioning who OCs are after noticing a feminine or masculine quality that OCs shouldn't have.

A) TW: OCs are blackmailed after their competitor finds out their actual gender. They're forced into doing certain things so the secret won't be leaked.
B) OCs competitor finds out their actual gender but doesn't make it known to OCs. One day, it's a competition and OCs are doing what they do best, until they fall by something their competitor planned. OCs actual gender is revealed to everyone watching and OCs are disqualified.