This may be a rule for during high school season practices? I can't imagine it would be enforceable otherwise.

Students may participate in team sport practice and contests as members of a non-school team provided no more than 5 student athletes, (i) who have participated in a contest the previous season as a member of one of their school teams in softball or (ii) who are incoming freshman, are rostered on the same non-school team, at the same time.