Green’s Dictionary of Slang

(Irish) excellent, first-rate; thus as an affirmative excl.

1922		Joyce Ulysses (1960) 291: That’ll do, game ball, Blazes Boylan said.
c.1940–5		‘Myles na gCopaleen’ Best of Myles (1968) 102: Come on down lower in the page and you’ll be game ball.
1948		P. Kavanagh Tarry Flynn (1965) 22: ‘Everything’s game ball,’ Charlie said, and winked.
1975		J. Ryan Remembering How We Stood 48: Is de grub all right? Grand. Game ball!
1981		(con. c.1920) P. Crosbie Your Dinner’s Poured Out! 54: There was one short question and answer rhyme, which went [...] ‘How’s your oul’ wan?’ ‘Game ball!’.
1998		J. O’Connor Salesman 104: ‘That’s gameball so,’ he said.
2000		F. Mac Anna Cartoon City 78: Say we bring the horse back tonight and it’s game ball and all that?
2004		P. Howard PS, I Scored the Bridesmaids 229: ‘There’s another twenty in it for you if you keep it closed,’ and he goes, ‘Game ball.’.