Act the part of a villain; take the blame for unkind behavior. For example, She can't bear firing an employee, so she relies on Jim to play the heavy. This colloquial term comes from the theater, where heavy has been used for a stern, serious role or that of a villain since the early 1800s.
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.