Selecting Defenses

[LeelandS]

We have had a lot of trouble finding clarification on the defense selection process. Additionally, we can't find a Q&A on the subject, and have had an embarrassingly great amount of trouble figuring out how to ask a question.

During the defense selection process, we are selecting the defenses our opponents will be facing. We understand that 1 defense from each group will be present on the field. Our issue is that, say both alliances want their opponent to have a portcullis (and the portcullis is available for selection because it is not in the group the audience is picking).

How is it decided which alliance will receive their pick of the portcullis, and who can't pick it? We've looked over as many rules pertaining to defense selection that we can find but we can't find clarification of picking priority or if there's a process/aspect of the picking process that we are missing.

Is the issue that we are misunderstanding the establishing of 1 defense from each group mean that a defense cannot be selected by both sides, or is it saying that each group will be represented, and the same defense from a group can be selected for both sides of the field?