The correct answer is: an acting crowd.
An acting crowd refers to a crowd or group of people who are highly emotionally charged when moving towards a goal. An example of an active crowd would be a group of protesters at a march or rally, protesting against an unfair law. In a protest or rally, the group gathered can be referred to as "an acting crowd" because the members of a protest are highly emotionally charged and passionate about the cause they are fighting for.