Green’s Dictionary of Slang

convincing ground n.

[the fighters attempt to ‘convince’ each other of the error of their ways]

(Aus.) a place at which prize or grudge fights are held.

[Aus]Bell’s Life in Sydney 7 Apr. 4/1: On our arrival there we received the office and lost no time in wending our way to the convincing ground.
[Aus]Baker Popular Dict. Aus. Sl.