A convincing ground was the name or journalistic euphemism for a place where sports were contested, having limited currency in the nineteenth century, predominantly in Australia and New Zealand.
It has been used to describe a boxing arena in Australia, a social sports ground in 1891, a cricket ground in New Zealand in 1862 and a trotting track in New Zealand in 1904.
Two placenames in Australia retain the name; Convincing Ground Road at Karangi, New South Wales and the Convincing Ground, a flat coastal area at Allestree near Portland, Victoria where a massacre of Aboriginal (Gunditjmara) people by whalers is thought to have occurred in 1833 or 1834.
References
Convincing Ground Wikipedia(Text) CC BY-SA