Black Friday: The science behind why people kill each other over TVs on the Friday after Thanksgiving

We're all hardwired for violence under certain conditions, and this one shopping day provides the perfect combination of them

Shoppers wrestle over a television at an Asda superstore in Wembley (REUTERS/Luke MacGregor)

What causes people to kick, shove and even stab each other on Black Friday?

Each year there are reports of violence during the Black Friday sales. Last year, in Philadelphia – the City of Brotherly Love, no less – two families fought until one of the women ended matters with a stun gun. In a New Jersey Walmart, a belligerent shopper had to be pepper sprayed by police. And in Virginia, one man slashed another with a knife in an argument over a parking spot. This year, there are sure to be similar cases. In the UK, at least two people have already been arrested after scuffles in supermarkets.

And why?

The reasons are primal.

We are all "hardwired" for violence under the right set of circumstances. Fortunately, those circumstances are rare (increasingly so), but do occasionally occur.

So what conditions set the stage for possible violence on Black Friday? The first is a valuable reward – something we are highly motivated to obtain. On Black Friday, the reward is a bargain. And people love bargains. In part, this is because we tend to view price reduction as a gain — as something for nothing. Consider that, shopping and saving at the very same time!

But getting a deal is also affirming, exciting, and allows us to enjoy products that would normally be out of our reach. People will wait overnight in freezing weather for the chance to get a good deal. They will also buy stuff they have absolutely no need for, simply because it is on sale. How many of us can look no further than the closet to see evidence of this?

That alone shouldn’t inspire people to violence though — a few more key ingredients are needed.

The second condition is competition. And the competition originates in the limited number of products that are typically offered at the most heavily discounted prices, the “door-buster” items. Not only are these items more desirable due to their larger discount, but there are typically only a small number of them available.

This means one shopper’s gain is another shopper’s loss, a psychological zero-sum game. Factor into that the sheer quantity of people waiting to rush once the doors open – last year Macy’s saw over 15,000 eager shoppers waiting to get in – and you have a level of competition like no other time of year.

Now we’re starting to talk about some classic violence-inducing conditions: massive competition for a very limited number of high-value resources. Our behavior, however, is also severely constrained by relevant social norms. That brings us to the third relevant condition: the presence or absence of norms that might promote or prevent violent behavior.

One of the norms that is relevant to situations involving scarce resources is the line-up norm. Lining up is a socially agreed upon alternative to a free-for-all for access to resources, and generally reduces violence.

The line-up norm, however, can sometimes inspire violence. Especially when someone butts in. This has been the cause of past Black Friday violence, and almost certainly will be again. The line-up norm is so powerful that even people in front of the person who butted in get upset. Violence in this case is a way of protecting the norm.

The line-up norm causes additional problems on Black Friday too, because, at a certain point, it no longer holds – when the doors open. The norm at that point is free-for-all.

Ironically, this norm is implicitly sanctioned by stores. They make a big fanfare of opening the doors, of letting the crowds rush in. They set a discrete date and time for the sale to start, and, very often, a limited number of heavily advertised door-crasher items. That’s not to absolve shoppers of any responsibility, but it is worth noting that the system is almost optimally designed to cause shopping mayhem.

With all those factors at play, it is perhaps a testament to our "better angels" that there isn’t more violence.

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