Green’s Dictionary of Slang

(Aus./N.Z.) a bowler hat.

1885		Bulletin (Sydney) 25 Apr. 13/2: We will dedicate a verse to him, in the hope that he may paste it in his hard-hitter for future guidance.
1893		Illus. Sydney News 23 Dec. 12/1: Dressed in a seedy grey tweed, ’lastic sided boots, and a brown hard-hitter hat.
1899		Queenslander (Brisbane) 10 June 1068/3: His hardhitter hat flew from his head and rolled down the aisle.
1901		H. Lawson ‘Buckolt’s Gate’ in Roderick (1972) 440: Jim sat in his shirt-sleeves, with his flat-brimmed, wire-bound, ‘hard-hitter’ hat on.
1911		Barrier Miner (Broken Hill, NSW) 8 Aug. 4/7: He removed his hardhitter from the sleeper’s head, upon which he placed his Dr Jim.
1925		Sydney Mail 15 July 8/1: It was the time of the ‘bowler’ hat, the ‘boxer,’ the ‘hard-hitter,’ the ‘plug hat,’ the ‘derby’ — terms synonymous, bul. varying according to environment.
1927		Brisbane Courier 11 Apr. 11/3: In the old country [...] the men’s costume would be [...] Beaufort coat and either topper or hardhitter.
1936		Courier-Mail (Brisbane) 22 Aug. 22/3: He wore a brown suit and a black hard hitter.
1940		F. Sargeson ‘Conversation with My Uncle’ in A Man and His Wife (1944) 31: My Uncle wears a hard knocker.
1942		Le Courrier Australien (Sydney) 5 June 7/1: You call a bowler hat a darby or hardboiled hat: we line it up as a boxer, bocker, hardhitter, eggboiler, plug hat, peadodger, bun or hap harry.
1951		D. Stivens Jimmy Brockett 29: He came out to meet me, wearing a hard-hitter and a fancy waistcoat.
1964		J.A. Lee Shiner Slattery 159: ‘Let me see myself in a knocker before I die.’ [...] Shiner put the hat on at a jaunty angle.
1972		G.W. Turner Eng. Lang. in Aus. and N.Z. 107: Now dated [...] numerous names for a bowler hat [...] bun hat, hard hitter, hard knocker.
1988		McGill Dict. of Kiwi Sl. 55/1: hard hitter bowler hat.
2003		McGill Reed Dict. of N.Z. Sl. [as cit. 1988].