1
general::
Be punished or blamed for something, as in I don't want to take the rap for Mary, who forgot to mail the check in time, or Steve is such a nice guy that he's always taking the rap for his colleagues. This slangy idiom originally used rap in the sense of "a criminal charge," a usage still current. By the mid-1900s it was Also used more broadly.
American Heritage Idioms
2
general::
Phrase(s): take the rap (for something)
Inf. to take the blame for (doing) something. • I won’t take the rap for the crime. I wasn’t even in town. • Who’ll take the rap for it? Who did it?, Phrase(s): take the rap (for someone)
Inf. to take the blame [for doing something] for someone else. • I don’t want to take the rap for you. • John robbed the bank, but Tom took the rap for him.
McGrawhill's American Idioms And Phrasal Verbs