Grace Spalding didn't spend the Friday night before her 21st birthday party drinking into the wee hours. She wound up in a hospital bed after a large, older man assaulted her in Brisbane's King George Square.

Philip Steven George Taua, 51, barrelled into his victim from behind on February 5, about 7.45pm, knocking her out when her head smashed into a bench.

A few months later he walked out of the Brisbane Magistrates Court with a $450 fine, a nine-month good behaviour bond and no conviction after pleading guilty to common assault and assault occasioning bodily harm.

That's no justice at all according to the corporate program manager, who is considering pursuing civil action.