I'll say it again - stop selling beer.
And give a marshal the right to have a person removed.
Most marshals don't want this right. Most are just volunteers who receive little to no training, especially in terms of crowd control. The events also wouldn't want the liability of entrusting volunteers with that job.
My dad has volunteered at a great many USGA and PGA-run events. I specifically recall he told me while working the WGC match play event that he had the authority to warn spectators (either due to behavior or inappropriate phone use) and also had the authority to call in an "enforcement team" of two security personnel who would escort offenders off the property if necessary. I wouldn't imagine that is unique to just that event, but I'm also sure it's easier for a marshal at the sparsely-attended WGC match play event to be aware of who a specific offender is than it would be for anyone at a very crowded NYC-area playoff event.