As indicated by its name, the pitches list exists for discussion among the "pitches" of collegiate Christian a cappella groups, and so membership in the list is reserved for such pitches.
The definitions and roles of "pitch" vary widely from group to group, and so the question of precisely who should have membership in the emailing list for "pitches" is not always easily answered.
In general, the one person whom a collegiate Christian a cappella group would typically send to a pitches' retreat (an ancient metric; when was the last one?) should be a member of the Pitches list. Some groups have "co-pitches" or some similar arrangement; it's definitely appropriate for co-pitches and the like to be members of the list.
There are many people who meet the above qualifications but who are not currently the official leader of a group in such a capacity (e.g., retired pitches and hyper-active group members); it is possible for such persons to be members of the list. In every such case, the membership of that person will need to becleared with the current list members and administrators. In general, decisions regarding membership in the list will be made conservatively and restrictively.