It is "awkward". It seems like you are avoiding saying the word "men". There are some words that are taboo in English, and we might use expressions of various complexity to avoid insulting people, and that's what it looks like you are doing if you use "the opposite gender".
From a strictly technical point of view it is also incorrect. "Gender" is a property of nouns in certain languages (such as Latin, French or German). It is sometimes by extension used to talk about people, but some consider that to be a misuse of the word. People have sex, not gender.
So keep it simple. Women (not females) chose to play netball, but it was unpopular with men. The comma helps but probably isn't required.