As David Harsanyi notes in The Blaze, being heterosexual is considered cheating by the league, and the players’ team suffered the consequences:

There’s certainly nothing wrong with the league. We have leagues for kids, women‘s leagues and men’s leagues. People should be allowed to assemble and play games with anyone they choose (as long as they don’t smoke!) and devise the rules of membership. Obviously there is no inherent difference between the athletic ability of gay, straight or bisexual men, so the strict rules governing sexual preference in this case make this a social event as well as competitive tournament.
In the end, the committee ruled that three of the five players were “nongay” and the team was stripped of its second-place finish. The piece goes into some length on the legality of this kind of exclusion, and explores some thorny questions about how to define who is gay.
But I dare to dream. And one day perhaps all Americans will play softball together.