Green’s Dictionary of Slang

(Aus.) an informer.

1943		Baker Popular Dict. Aus. Sl. (2nd edn).
1946		Mail (Adelaide) 9 Mar. 3/2: In January, the following year, a ‘fizz’ — a police informer— dropped a hint that caused detectives to renew their efforts.
1957		J. Waten Shares in Murder 25: This was Brummel's speciality. He had turned more criminals into police spies than any other officer Fields had ever known. No one had more fizzes in his hands .
1990		Tupper & Wortley Aus. Prison Sl. Gloss. 🌐 Fizz. An informer (Vic).
1996		(con. 1964-65) B. Thorpe Sex and Thugs and Rock ’n’ Roll 195: ‘I’m not asking you to be a fiz [...] a grass’.
2013		D. Whish-Wilson Zero at the Bone [ebook] Riley’s attitude was also part of the game. A matter of saving face. He was a fizz.
2023		D. Whish-Wilson I Am Already Dead 201: ‘[S]etting up of a team [...] , going back to the sex offenders, working our fizzes’.