The club have the final say who gets into the ground or not, they are judge and jury re any alleged infringements of the ground rules, code of conduct etc not the police. So the club can ban any individual or group they want from the ground, suspend ST's etc
If however these infringements also break any current laws in force then yes the police should be involved as they have a duty of care re public saftey, although i would not hold my breath waiting for that to happen.
Nothing is difficult here, how much cash are the club willing to waste on fines and sanctions before they take decisive action, instead of sitting back paying the fines and hoping the problem will go away.