1
general::
A scapegoat, as in This department's always been the whipping boy when things don't go well. This expression alludes to the former practice of keeping a boy to be whipped in place of a prince who was to be punished. [Early 1900s]
American Heritage Idioms
2
general::
Phrase(s): a whipping boy
Fig. someone who is punished for someone else’s misdeeds. • The president has turned out to be the whipping boy for his party.
McGrawhill's American Idioms And Phrasal Verbs