In this clip, what evidence is there to suggest that the group has defined roles for the discussion?

As it is not possible to have access to the clip, it will not be possible to promote an answer with exactness, however I will try to help you in the best possible way.

To define discussion roles in a group, we must be able to observe that each person within that group was responsible for a topic, which will be inserted into the discussion, so that each person must assume their role defending the topic to which they were assigned.

it limits peoples’ voting options. hope it : )