Vivek Ramaswamy emerged as a popular target early in the debate, drawing cheers from the audience when he introduced himself.
"Let me just address a question that is on everybody's mind at home tonight," the biotech entrepreneur said. "Who the heck is this skinny guy with a funny last name?"
Former Vice President Mike Pence called him a "rookie," saying people should not elect people without experience.
Christie accused Ramaswamy of trying to imitate Barack Obama and said the country had already tried that.
"The last person in one of these debates who stood in the middle of the stage and said, 'What's a skinny guy with an odd last name doing up here?' was Barack Obama, and I'm afraid we're dealing with the same type of amateur," Christie said.