For future reference, here is a link to the Rules forum (might require you to be a current PSI member to view):http://forums.poetryslam.com/index.php/board,5.0.html
I think the "cheerleading" section Ed is referring to might be the Gag Rule (or, colloquially, the "Bay Area" rule). This rule governed the behavior of teammates in the audience: teammates, coaches, and SMs were barred from leading or coaching the audience in response to a performer on stage. This rule was struck around 2008, about the time indies were removed from NPS; behavior of this type at NPS now may cause the poem to be assessed as a group piece. The rule was removed since the rules on what constitutes a group piece and the rule about not influencing the audience (above) appeared to cover the same ground.
I do not see a thread, either current or old, in the Rules Forum about call and response. I would be happy to join in a discussion over there, or, with Ed's permission, could arrange to have this thread moved to the Rules Forum so we can continue there.