In some states, AFAIK the "women-only gym" is allowed, but in others it isn't. The point, if I remember correctly, is "exercise requires such compromising clothes and positions, that the right to personal privacy trumps the right to not be discriminated based on gender". And even then, this is not a 100% clear case. Toilets and physical activity follow a similar (although less polemic) pattern.
Having said that, and as far as I understand, you need to show that discriminating based on gender is so important for your activity that it can't be done in any other way. My gut feeling is that, should anyone sue Leap, clearing that barrier would not be trivial.
I would appreciate a lawyer's point of view, and was hoping that Leap had already talked to one that could give a properly researched answer.
Edit: I found a very interesting article[1] about the law when it comes to all-female health clubs. As expected, the conclusion seems to be "it's complicated".
[1] http://digitalcommons.law.yale.edu/cgi/viewcontent.cgi?artic...
> Gender is a protected class
Which means that businesses doing public accommodation are restricted from discriminating, but 'private clubs' (such as the Boy Scouts), who have a narrowly tailored interest that is benefitted by discrimination against a protected class is generally allowed (subject to variances within state law).
For example, a group for men who have been sexually molested by men would likely be considered presumptively lawful, but a group for men who also happen to be car salesmen would likely not be.
There are a number of details that need to be considered as well, as (loosely) prescribed by _Rotary Club of Duarte[1]_, such as exclusivity (it can't be publicly available to be overheard), and purpose (already covered), but if neither conditions are met, and a state law prohibits such discrimination, then it meets (at least) a rational basis standard.
Any man taking such an action in 2018 would likely lose their career over it.