Taken directly from the Presidential Debate Contract Memo of Understanding Section 7, Additional Rules applicable to the October 16th debate.
"The moderator will not ask follow-up questions or comment on either the questions asked by the audience or the answers of the candidates during the debate or otherwise intervene in the debate except to acknowledge the questioners from the audience or enforce time limits, and invite candidate comments during the 2 minute response time."
Oh dear, I do believe Miss Crowley severely violated that rule. I think I preferred Jim Lehrer from the first debate to Candy Crowley because he was so clueless that at least he did not flagrantly violate the rules in his role as moderator.. Here is what the Washington Post had to say about Ms. Crowley's egregious conduct last night.