Green’s Dictionary of Slang

(N.Z.) courage.

1988		McGill Dict. of Kiwi Sl. 10/2: a bit more apple used to indicate the need for more courage by commentator during inaugural Rugby World Cup, Wales versus Canada, 3 June 1987.
2003		McGill Reed Dict. of N.Z. Sl. 12: apple [...] 2. Guts or intestinal fortitude.
2001		D. Looser Boobslang [U. Canterbury D.Phil. thesis] 7/2: apple n. courage, nerve, 'balls'.