Violence has marred the annual “Black Friday” crush of bargain hunting that traditionally kicks off the U.S. holiday shopping season following the Thanksgiving Day holiday.

Authorities say a woman at a Wal-Mart store in Los Angeles, California pepper-sprayed other shoppers in order to gain an edge on customers seeking to purchase Xbox video game consoles on sale. As many as 20 people were injured in the Thursday night attack, many complaining of burning in their throats and skin and eye irritations. Investigators are reviewing security tapes in an effort to track down the woman, who could face felony battery charges if caught.

Several shooting incidents also were reported at Wal-Mart stores and other shopping centers across the country. At least two of the incidents appeared to be robbery-related.

Black Friday is the day many stores sharply discount high-priced items such as electronics and the latest new toys. Its name signifies retailers' expectations of high sales, as profits were once recorded in account books in black ink, while losses were recorded in red.

Stores also open their doors hours earlier than usual, which helps foster excitement among bargain hunters.

Black Friday is one of the most important days for retail chains because it indicates what they can expect during the next month of holiday shopping — the most lucrative time of year for them.

But not everyone is in favor of the phenomenon. Demonstrators with the anti-capitalist Occupy Wall Street movement were encouraging people to take part in “Buy Nothing Day,” a day of protest against consumerism.