In 2011, psychologist Mina Cikara and colleagues at Princeton University put Red Sox and Yankees fans in an MRI scanner and showed them baseball highlights. When a fan’s rival team failed, a reward region of the brain called the ventral striatum became more active, the same region linked to pleasure and reward. Derby day, it turns out, is not really about the football at all.
Key Takeaways
- Rivalry runs on identity, not results. Fans gain self-esteem from group belonging, which is why a rival’s failure can feel as good as your own team’s win.
- A 2011 brain-imaging study of 18 baseball fans found that watching a rival fail activated the brain’s reward region, even when the rival lost to a third team.
- The fiercest rivalries combine geographic closeness, shared history, and an outside marker like class, religion, or politics, not football quality alone.
- Crowd psychology explains why normally reasonable fans behave differently on derby day, a process psychologists call deindividuation.
- Understanding the psychology behind a rivalry does not excuse the worst of it, but it explains why these fixtures never feel like just another match.
It Starts With Identity, Not the Team
Social identity theory, first developed by psychologist Henri Tajfel in the 1970s, argues that people naturally sort themselves into groups and draw part of their self-esteem from those groups doing well. A football club is one of the easiest identities to adopt: it is inherited from family, tied to a place, and worn visibly on a shirt.
Once that identity forms, a rival club is not just an opponent, it is the clearest possible “them” against your “us.” Beating a mid-table side you have no history with barely registers. Beating the rival confirms something about who you are, which is why the result matters so disproportionately more.
Why Losing to a Rival Hurts, and Winning Feels So Good
The study, published in Psychological Science by Cikara, Matthew Botvinick and Susan Fiske, involved 18 avid baseball fans, 11 of them Red Sox supporters and 7 Yankees supporters. It found something specific: fans showed a reward response when their rival lost to a neutral third team, the Orioles. It was not only about their own club winning. It was about the rival failing.
The researchers also asked how likely each fan would be to heckle, insult, threaten or hit a rival fan. Activity in the ventral striatum when the rival failed was linked to that willingness to harm rival fans (Princeton). That does not mean every fan with a strong rivalry is a hooligan waiting to happen, but it shows why rivalry-driven emotion can tip past normal sporting disappointment into something closer to hostility.
How Strong Is the Evidence?
It is a small study of baseball fans, not football fans, and the authors describe the link between brain activity and willingness to harm as a correlation, not proof of cause. The finding is best read as a useful illustration of how rivalry works, not a rule that applies to every supporter. The same social identity pattern shows up around the world, from the Mashemeji derby in Kenya to the Nigeria vs Ghana rivalry in West Africa.
The Ingredients That Turn Local Sides Into Enemies
Not every local derby becomes a genuine rivalry, and researchers who study fandom point to a few factors that tend to show up together in the fiercest ones.
Geographic Proximity
Clubs that share a city or a region compete for the same fans, the same bragging rights, and often the same physical territory. Distance makes a rivalry easier to shrug off. Two clubs sharing a postcode cannot avoid each other, which is the story of the Soweto derby between Kaizer Chiefs and Orlando Pirates.
A History Worth Repeating
A single bad result rarely creates a lasting rivalry. What does is decades of meetings with something on the line, title deciders, relegation battles, cup finals, repeated often enough that each new game gets read through the lens of every previous one.
An Outside Marker
The rivalries that go beyond football, Celtic and Rangers, Boca and River, tend to have something else attached to the football: religion, class, or politics. That extra layer turns a football result into a proxy for a bigger argument that was never really about ninety minutes. Algeria and Morocco show it at national level, in a rivalry where football and politics are tangled together.
This is also why some local derbies stay relatively good-natured. Liverpool and Everton share a city, a long history, and even families, yet their fixture was known for decades as the “friendly derby” precisely because it never picked up that extra layer of religion, class, or politics that Glasgow’s did. Proximity and history alone can make a fixture big. It takes that third ingredient to make it genuinely bitter.
Why Derby Day Feels Different
Psychologists have a name for how normally sensible people behave differently inside a large, emotionally charged crowd: deindividuation. Wrapped in a stadium full of people who share the same identity and the same grievance, individual fans feel less personally accountable for how they act, which is part of why chants, gestures, and behaviour on derby day go further than they would anywhere else.
None of this makes the ugliest moments in football’s rivalry history acceptable. But it does explain why fans who are perfectly reasonable on any other Saturday lose their minds completely on derby day. It is not really about the match. It is about who they are, and who they are not.
Where to See It in Practice
For the history behind the rivalries mentioned here, see our ranking of the world’s fiercest derbies, the story of England vs Scotland, the oldest international fixture, and the culture of football ultras, where group identity is on show every matchday.