How much crazier can Black Friday get?

NEW YORK — Pepper-sprayed customers, smash-and-grab looters and bloody scenes in the shopping aisles. How did Black Friday devolve into this?

As reports of shopping-related violence rolled in this week from Los Angeles to New York, experts say a volatile mix of desperate retailers and cutthroat marketing has hyped the traditional post-Thanksgiving sales to increasingly frenzied levels. With stores opening earlier, bargain-obsessed shoppers often are sleep-deprived and short-tempered. Arriving in darkness, they also find themselves vulnerable to savvy parking-lot muggers.

Add in the online-coupon phenomenon, which feeds the psychological hunger for finding impossible bargains, and you've got a recipe for trouble, said Theresa Williams, a marketing professor at Indiana University.

"These are people who should know better and have enough stuff already," Williams said. "What's going to be next year, everybody getting Tasered?"

Across the country on Thursday and Friday, there were signs that tensions had ratcheted up a notch or two, with violence resulting in several instances.

A woman turned herself in to police after allegedly pepper-spraying 20 other customers at a Los Angeles-area Walmart on Thursday in what investigators said was an attempt to get at a crate of Xbox video game consoles. In Kinston, N.C. a security guard also pepper-sprayed customers seeking electronics before the start of a midnight sale.

In New York, crowds reportedly looted a clothing store in Soho. At a Walmart near Phoenix, a man was bloodied while being subdued by police officer on suspicion of shoplifting a video game. There was a shooting outside a store in San Leandro, Calif., shots fired at a mall in Fayetteville, N.C. and a stabbing outside a store in Sacramento, N.Y.

"The difference this year is that instead of a nice sweater you need a bullet proof vest and goggles," said Betty Thomas, 52, who was shopping Saturday with her sisters and a niece at Crabtree Valley Mall in Raleigh, N.C.

The wave of violence revived memories of the 2008 Black Friday stampede that killed an employee and put a pregnant woman in the hospital at a Walmart on New York's Long Island. Walmart spokesman Greg Rossiter said Black Friday 2011 was safe at most of its nearly 4,000 U.S. stores despite "a few unfortunate incidents."

Black Friday — named that because it puts retailers "in the black" — has become more intense as companies compete for customers in a weak economy, said Jacob Jacoby, an expert on consumer behavior at New York University.

The idea of luring in customers with a few "doorbuster" deals has long been a staple of the post-Thanksgiving sales. But now stores are opening earlier, and those deals are getting more extreme, he said.

"There's an awful lot of psychology going on here," Jacoby said. "There's the notion of scarcity — when something's scarce it's more valued. And a resource that can be very scarce is time: If you don't get there in time, it's going to be gone."

There's also a new factor, Williams said: the rise of coupon websites like Groupon and LivingSocial, the online equivalents of doorbusters, which usually deliver a single, one-day offer with savings of up to 80 percent on museum tickets, photo portraits, yoga classes and the like.

The services encourage impulse buying and an obsession with bargains, Williams said, while also getting businesses hooked on quick infusions of customers.

"The whole notion of getting a deal, that's all we've seen for the last two years," Williams said. "It's about stimulating consumers' quick reactions. How do we get their attention quickly? How do we create cash flow for today?"