"If we really cared about safety and fairness in sports, we’d be breaking down barriers facing girls at every level," writes Megan Rapinoe.

How do you enforce who is “girl enough” to play sports? In my home state of Washington, the most extreme proposal of its kind is before voters on the November ballot. Measure I-638 would require all girls—but not boys—to be medically sex certified before they can play sports.

In a country rife with sexual assault, young girls would have to undergo invasive inspections of their genitals, or pay for a DNA or hormone test, as part of their school sports physicals. Doctors say genital inspections are not only medically unnecessary to play sports, they can traumatize and physically harm young girls.