What does it mean to pull no punches?

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.”

Will not pull any punches?

If you say that someone does not pull their punches when they are criticizing a person or thing, you mean that they say exactly what they think, even though this might upset or offend people. She has a reputation for getting at the guts of a subject and never pulling her punches.