Green’s Dictionary of Slang

hammer n.2

[play on knock v. (2a)]

1. an unashamed lie.

[UK]Partridge DSUE (8th edn) 524: [...] from ca. 1840.

2. an unjust or carping criticism.

[US]W.J. Kountz Billy Baxter’s Letters 20: She could build the best battleship Dewey ever saw with her little hammer.
[US]K. McGaffey Sorrows of a Show Girl Ch. xii: She always treated them with a calm air of condescension, and they would lay for the chance to get in a hammer.

In compounds

hammer duet (n.)

(US) a fig. ‘duet’ formed of any group devoted to negative criticism.

Ade ‘The Modern Fable of What Horace Stood For’ in St Paul Globe (MN) 18 Jan. 30/4: For a Hammer Duet, the Men’s Club makes the Boiler-Works seem like the Hush of Death.
[US]Columbus Jrnl (NE) 17 May 6/3: A Hammer Duet. ‘That fellow Fibbers,’ said Jaggson contemptuously. ‘He seems to be afraid of the truth.’ ‘Well you know, replied Billson, ‘it is always best to be cautious of strangers ’.

In phrases

throw the hammer (v.)

1. to obtain money under false pretences.

[UK]J. Ware Passing Eng. of the Victorian Era 245/2: Throwing the hammer (Low Military). Erotic. Obtaining money under false pretences.

2. (US) to criticize negatively, to disparage.

[US]‘Hugh McHugh’ John Henry 69: Dale can throw the hammer and get back to his safety deposit vaults without a scratch.
[US]‘Hugh McHugh’ It’s Up to You 12: Percy used to be a dramatic critic [...] and he had the reputation of being able to throw the hammer farther than any one else in the ‘Knocker’s Union’.
[US]E. Freeman ‘The Whirling Hub’ in Afro-American (Baltimore, MD) 16 Feb. 15/1: Joshua (Nonchalant) Bonds [...] is to ‘throw the hammer’ to a certain Tush-Hawk — City smart aleck to you.