Encourage your adversary to be complacent by acting as if it wouldn't occur to you to challenge him or you fully realize you can't challenge him because you couldn't win. As military strategy has long held, if the opposition force is too large to face directly, try to make them travel through a narrow pass, so you can pick off the whole line, however long it may be, one by one, as each comes through the pass. This same strategy recently was used by seven infamous prison inmates, who recently escaped from the maximum security Connally unit in Texas, by initially waiting for their guards to go out to lunch, then overpowering them one by one, as they returned. Meetings played out before observers, like departmental meetings or board meetings, form just such a narrow pass. Rules are in place and others to enforce them.
Participants have to be called on to speak, one by one.
Confront your adversary individually, or if it is a group, confront the leader, calmly, firmly and with documentation, and it is unlikely that the others will jump in to defend him. It is easy to bully in an ad hoc group. In a public meeting, where your actions are being watched and possibly recorded, it is difficult to stand up for something which is patently against the rules and already documented as such. Turning back your adversaries is not enough in itself. You must use your victory to propel your policies in your organization and achieve the success of its mission.