What is Shifting?

Legal Definition
Changing; varying; passing from one person to another by substitution. "Shifting the burden of proof" is transferring it from one party to the other or from one side of the case to the other, when he upon whom it rested originally has made out a prima fade case or defense by evidence, of such a character that it then becomes incumbent upon the other to rebut it by contradictory or defensive evidence.
See also
-- Black's Law Dictionary