Hiring security guards for your event can be a good way to cut down on trouble. Just the presence of guards overseeing the event can dissuade some people from becoming belligerent. When you contact the security company to arrange for guards to work at your event, you'll need to give the company more information than just the dates, times, and location.
What's the Perimeter of the Event Space?
Security guards have jurisdiction only in the space they've been hired to cover. They can also only make citizens' arrests in that jurisdiction. They can't do much outside that perimeter except for following general citizens' arrest laws, which tend to be very restrictive. Within the event perimeter, the guards still have to follow those laws, but they have a little more authority as the guards have been authorized to act as a security force in a certain space.
If the event is taking place at a community center or another public space, you need to know exactly what constitutes the event perimeter. It might not be the same as the perimeter of the center, if the center is particularly large. Contacting the center management and discussing where the event can and can't spill into will help.
Do You Want Armed Security?
You need to decide now if you want armed security. Even if the guards don't draw their firearms, the mere presence of guns can be distressing to some. On the other hand, if your event will be in a sketchy area, or if you're worried about troublemakers doing more than just being rowdy, having armed guards could be reassuring.
How Much Security Coverage Do You Want?
You can hire as many security guards as you want, as long as the company has the staff. But think about how many you really need and how many would make you feel protected. You may decide that just a couple wandering around a small event is enough, or you may want a visible presence that leaves no part of the event unguarded. Take breaks into account, too, as the guards will need to use the restroom or have a meal break during longer events.
After getting space information from the management of the center where you're holding your event (if the event isn't at your home), contact companies that provide security guards and talk to them about who can cover what space and what the guards can do. Arrange for event security patrols if you think they will add security to your next big event.