In terms of banning people from the parks, it's relatively easy. The term WDW Managers and Cast Members use is a bit more accurate, "trespassed." From a legal perspective, the Orange County Sheriff's Department issues what is called a "tresspass warrant." It is a legally binding document that prohibits a person from entering Walt Disney World property. Doing so results in an immediate arrest, or at the very least, a severe warning. Most of the time these are issued for at LEAST one year, but often five.
In addition, depending on the severity of the offense causing the trespass warrant, you might get a ride to downtown Orlando directly from the Magic Kingdom to the Orange County booking center and jail (let me just tell you how fun it is to drive a family there from the park, when their loved one has just been arrested).
From a WDW operations side, there is no sure fire way to "ban" somebody. The ticketing system (ATS) has a list of people who are banned from purchasing tickets, and Guest Relations maintains a separate guest service recovery tool that documents GR and Service abuses. If either of these are flagged when a cast member enters a persons name, they notify security.
Personally, I've had to have two people thrown out of the park and trespassed. One of which was a guy who was using fake IDs to obtain comp tickets with an array of fake name and fake service issues/problems. The other was a guy who lost his mind on gay days, using obscene names and threatening me, grabbing my tie, if I didn't do something to get these "f'ing f**gots out of the park." Awful guy and deserved to be banned from the most Magical Place on Earth. :animwink: