Behave unrestrainedly, hold nothing back, as in The doctor pulled no punches but told us the whole truth. This expression comes from boxing, where to pull one's punches means “to hit less hard than one can.” This idiom, too, has been applied more generally, as in They decided to pull their punches during these delicate negotiations. [First half of 1900s]
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.