Skip to main content

Verified by Psychology Today

5 Reasons Why Large Crowds Turn Violent

Social psychology research helps explain why peaceful protests can turn ugly.

Free Photos/Pixabay
Source: Free Photos/Pixabay

When large groups gather for party, protest, or sports, there is always the possibility that things can turn quickly from peaceful productivity to dangerous confusion. Many people do not realize that there are some pretty reliable factors that contribute to crowd violence around the globe. social contagion, anonymity, emotions, weather, and anxiety.

1. Social Contagion

The most important thing to know is that social contagion is almost always a contributing factor when peaceful protests turn disorderly. Social contagion refers to the spread of inappropriate behaviors simply because crowd members see others engaging in them. When you see someone throwing a rock through a store window the action becomes valid. The actions of a few people in a crowd of thousands may legitimize the violence. And there is a sense of “this is OK to do right now” because people around me are doing it.

Social contagion works for good and evil. Good: Everyone loves to participate in “the wave” at a football game. It is usually started by one or two few boisterous fans, but the numbers grow into the thousands once the behavior is noticed and it seems like a low-cost activity to join in. Bad: Unfortunately, the same psychology applies to mobs and violence. Breaking store windows might seem unthinkable if you are walking around by yourself, but in the context of the crowd, the same individual might make the calculation that it is low-risk because there is safety in numbers.

2. Anonymity

Don’t underestimate the power of anonymous faces. Social psychology studies demonstrate that people, even children, are capable of acting in aggressive ways when identity is concealed. We cannot be held accountable if we are not identifiable. Wearing a mask helps to deindividuate us and it is much easier to make transgressions. Anonymity, or “deindividuation” as psychologists say, is especially relevant in current protests that take place in the midst of a mask-wearing pandemic. Even peaceful people who would normally not wear a mask to a protest are forced to take on some anonymity due to the pandemic.

Additionally, we often struggle to read minds and intentions when we cannot see someone's face. Masks interfere with our natural ability to glean vital information from the face. If you are trying to assess the emotional state of someone it can be frustrating if you are an adult and it can be terrifying for a child. The face summarizes so much useful information about a person. Humans for several thousand generations have been assessing faces to obtain critical social data. That is why it is sometimes hard to gauge how a person is feeling over the phone or via text/email.

3. Emotions

When crowds assemble, there is usually an emotional thread that runs through them all. When fans celebrate a sports victory (or commiserating over a loss) or citizens attend a political protest emotions tend to run high. There is a different psychology to celebrating or protesting alone than when we do the same thing in a crowd of hundreds or thousands. It is a different state of mind. When people are in a state of emotional extremes, they don’t always make the same decisions they would if they were emotionally calm and by themselves.

4. Weather

One study found that the probability of a baseball pitcher hitting a batter with a ball increases as the temperature goes up. The pitchers weren’t losing the ability to control where the ball goes (the number walks issued was the same across heat levels) but they were feeling frustrated. The summer weather, combined with months of quarantine, is a dangerous mix. Lots of people have been caged inside and now they are out in massive crowds for the first time in a while. All it takes is one or two people to initiate something bad.

5. Anxiety

Pre-existing anxiety levels do not help. Between school, work, terrorism, bullying, and debt there is a lot for Millennials and Generation Z to worry about. According to data from NAMI (National Alliance on Mental Illness), 42 million Americans, or 18%, live with anxiety disorders. PTSD, panic disorder, and phobias all fall into this category. I’m not saying mental illness is the reason some peaceful protests erupt into violence, but we shouldn’t underestimate the impact of anxiety and stress on impulse control. People are anxious these days for a variety of reasons and losing your grip on what is right vs wrong is more likely when you are tired, stressed, and angry.


Harrigan, N., Achananuparpb, P., & Lim, E.P. (2012). Influentials, novelty, and social contagion: The viral power of average friends, close communities, and old news. Social Networks, 34, 470-480.

Larrick, R. P., Timmerman, T. A., Carton, A. M., & Abrevaya, J. (2011). Temper, Temperature, and Temptation: Heat-Related Retaliation in Baseball. Psychological Science, 22, 423-428. DOI: 10.1177/0956797611399292

Tsikerdekis, M. (2013). The effects of perceived anonymity and anonymity states on conformity and groupthink in online communities: A Wikipedia study. Journal of the Association for Information Science and Technology. 64, 1001–1015. doi:10.1002/asi.22795.

More from Kevin Bennett Ph.D.
More from Psychology Today
More from Kevin Bennett Ph.D.
More from Psychology Today