Green’s Dictionary of Slang

1. (Aus.) an excuse.

1941		Baker Popular Dict. Aus. Sl.
1959		D. Niland Big Smoke 210: Georgie Barber felt himself being drawn in, but he fought against it. It might be a square-off.

2. (Aus.) a bribe, a pay-off.

1991

R.G. Barrett Between the Devlin 41: ‘The estate agent said to give you this [i.e. A$200]. I think it’s a bit of a square-off from the owner’.