Is it legal to import replica NFL jerseys from China?

Yes, it is legal only if you have no intention on reselling them. All of the nation's Federal Laws center around selling of counterfeit goods. In California the closest penal code dealing with counterfeit goods is PC 350 which only addresses selling of these goods. So if you order a typical batch order of 10 jerseys from China there is nothing suspicious about that. But if you order 1000 jerseys, well...