I was inspired by the Euro 2016 recently - what about crowd mentality?
It could work like this:
1. There are many members of a certain race or several races that show similar values - in case of mentioned sports - wanting a certain team to win.
2. They all want the same thing and share their zeal.
3. These creatures can become a temporary group, inspired by a certain event. Imagine something like this - everyone is supporting a certain team, and one individual shouts for the other one. Instantly, everyone within earshot migh want to kick that person and they form a group to do so.
4. Other examples might be people in a town hating elves after and elf murdered a member of their race. Suddenly, they might form ad hoc rioting groups, having the same goal - to slaughter elves or drive them out of their town. When they all really hate elves, they might not even need a good reason, someone could shoult "kill elves, they are hiding all the gold and slaughter our children", and some will react without much consideration.
5. The point is that groups can form ad hoc if certain conditions are met, they share similar values and goals, even short term ones. Such groups can work together, without prior planning or organizing and perhaps under leadership of those who are the strongest or can shout loudly enough. Those will disband after some time or after they are satisfied with what they did - as when they kill the enemy supporter or slaughter all elves in the elven district.