People were going to "take to the streets" with or without the exemption. By working with organisers the police had some control.So all you have to do is infer if you don't get your way you will get violent then cool, if we can't go to the footy etc let's just let it known there will be a showdown with police then and we will all be back at the footy right?
If people want to go to the showdown, without getting an exemption, the only control needed is to not open the gates to the oval.