Even where no official rules keep them out of baseball, girls face enormous pressure to switch to softball. “They get chased right out of middle-school baseball,” said Jennifer Ring, the author of “Stolen Bases: Why American Girls Don’t Play Baseball,” whose daughter fought to play in high school and played a season on Vassar College’s Division III men’s team. When a girl persists in playing, Ms. Ring said, “you can’t count on it being a good experience, because you have to explain why you’re even there.”

Last year, 474,791 American boys played high school baseball, according to the National Federation of State High School Associations; 1,259 girls did. In some cases these girls were the only ones in their entire state. No college scholarships lie ahead, as they do in softball. Without the development of skills and talent at the high school and college level, a national women’s baseball team that plays in a World Cup will be treated as little more than a curiosity, struggling to find the attention it deserves.

What if we just admitted that softball and baseball are not, in fact, “separate but equal” but entirely different sports? There is no rational basis to claim that girls can’t throw overhand, run 90 feet between bases or handle a hardball. And there is no reason but sexism to prevent them from doing so.