Unfortunately for local Philadelphia authorities, not to mention municipal and private property owners, the wildness didn’t end at the game’s edge. Though most Philadelphia Eagles fans took the streets to revel in a historic Super Bowl win, some used the opportunity to riot. They flipped over cars, climbed up (and literally removed from the ground entirely) street poles, broke store windows, went running around naked in public wearing bird masks, and, in one of the more unfortunate expressions of fandom I’ve had the displeasure to read about, ate actual horse feces—in essence, destroying parts of their own home town (and dignity) in the name of celebrating their team’s first Super Bowl win.

I just got hit with a parking light pic.twitter.com/FflzyY5JDe

— rone’s gamblin corner (@rone) February 5, 2018

https://twitter.com/LacesOutShow/status/960389472012599297

Eagles fans have built up a reputation for being a rowdy, aggressive, and generally intense crowd. But they’re far from the first group of sports lovers to take things way too far in the name of victory. Which raises the question… What’s up with that?

Let’s take a little dive into the psychology of aggression and crowd behavior to better understand why Philadelphia, and so many other cities’ sports fans, respond in such a twisted and seemingly counterproductive way to their own successful conquests.

This essay appears in today’s edition of the Fortune Brainstorm Health Daily. Get it delivered straight to your inbox.

Your brain’s pleasure center is weird—and self-feeding

Conventional psychological wisdom used to dictate that acts of violence and aggression—you know, like, repeatedly punching a police horse—were almost exclusively motivated by fear, anger, and other negative emotions.

But more recent research finds that positive emotions which trigger the brain’s pleasure and rewards centers are equally strong drivers of destructive behavior, according to Dr. David Chester, an assistant professor of psychology at Virginia Commonwealth University who specializes in the sociological and biological mechanisms that drive aggression.

“Aggressive behavior, property damage, is actually pleasant behavior—it feels good for a lot of people,” Chester told Fortune in an interview. “When you win in sports, the brain tends to respond to it like it would if you received money, or a tasty beverage, or a drug that you particularly like. It recruits the brain’s reward circuits, which are multiple parts of the brain that include the vental tegmental area, or VTA, the ventral striatum, and the ventromedial prefrontal cortex, or vmPFC.”

This very biological effect of winning has significant consequences that could sway your behavior long after the game is over and victory secured. “Now what you’ve done is you’ve heightened the activity in the rewards circuit. So now, when you go out into the world, you’re going to be pursuing rewarding behaviors that you normally wouldn’t in your daily life, because you’ve cranked that part of the brain up to 11,” Chester explains.

Herd behavioral science plays a major role in this phenomenon, too. Social identity is an extremely strong (and in many cases critical) part of human existence. People need each other to strive and survive; but, in the case of large sporting events where individuals self-segregate into specific tribes, the “de-individuation” effect can lead to a type of mob mentality.

“The line is fuzzy between personal success and group success,” says Chester. “We experience teams wins like we ourselves won.” That lends to an effect called “identity fusion,” wherein it can become almost impossible to separate an individual from the group. “It’s like trying to get the eggs out of the cake mix once they’re already in there… People can basically end up acting like a school of fish.”

Alcohol, and men, make all of these things worse

Women have been claiming a larger and larger share of the NFL fan base in recent years. But football fandom still skews about 55% male—and that in and of itself raises the stakes for pandemonium following something like a Super Bowl win.

The U.K. government’s Cabinet Office commissioned a safety and emergency response report from the University of Leeds in 2009. The findings touched on a number of factors that could lead to riots and other dangerous mob behavior, including after soccer games. Two of the biggest drivers of violence and general havoc? Men, and alcohol.

“Be aware that there is greater potential for male dominated crowds to behave in a more aggressive manner in comparison to female-dominated crowds, mixed gender crowds, or crowds with a high proportion of family groups,” wrote the report authors, adding that intoxication is an obvious risk factor for violent behavior.

Chester’s research has produced similar findings when it comes to alcohol. “Drinking and acting aggressively actually have similar effects on the brain, so it acts as a positive feedback loop,” he says. Alcohol consumption shuts down the brain circuitry which promotes inhibition while boosting reward-seeking behavior; so does violence. So drinking essentially puts even more gas on a biological fire that’s already raging inside your head when you win and want to let loose.

The response to rioting is important, too

We’ve established that people can do some really, really dumb things as an outlet for their happiness. But the way that law enforcement engages with an unruly crowd is equally significant.

Poor crowd management has led to tragedies like the Hillsborough stampede of 1989, when 96 people died and more than 700 were injured in a misguided attempt to lock hoards of fans in a soccer stadium into pens.

Which is why this Philly cop probably had a better approach to dealing with the Eagles mob:

Happiest @PhillyPolice officer, Mark Lapenta, of the 22nd District, celebrating with fans at @TempleUniv pic.twitter.com/44Ia9F3gvR

— Robert Moran (@RobertMoran215) February 5, 2018

This isn’t to say that all types of rioting are created equal. While there’s still research to be done on the biological underpinnings of violent protests against, say, racial injustice versus winning the Super Bowl, the two types of activities clearly have very different purposes and goals, says Chester. But it’s important to recognize that happiness can be just as much of an instigator as anger. So celebrate safely, Philly fans.