LOS ANGELES (AP) — A woman trying to improve her chance to buy cheap electronics at a Walmart in a wealthy suburb spewed pepper spray on a crowd of shoppers and 20 people suffered minor injuries, police said Friday.

The attack took place about 10:20 p.m. Thursday shortly after doors opened for the sale at the Walmart in Porter Ranch in the San Fernando Valley.

The store had brought out a crate of discounted Xbox video game players, and a crowd had formed to wait for the unwrapping, when the woman began spraying people "in order to get an advantage," police Sgt. Jose Valle said.

"Faces were red," shopper John Lopez told ABC News Radio. "This one guy was coming up to my wife going, 'Call an ambulance! Call an ambulance!'"