sling mud at
Insult or discredit someone, as in The paper became famous for slinging mud at movie stars. This term replaced throw mud at, which dates from the second half of the 1700s.
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.