Add event or game limits on the Registration Settings page under Additional Options.
Event limit: This will set the total number of events that attendees can enter. There is a Min Events limit option which designates the minimum number of events an attendee must enter, and there is a Max Events limit option which designates the maximum number of events an attendee can enter.
Game Limit: This will set the number of games that attendees can enter. For example, if your tournament includes Melee singles and doubles as well as Smash Ultimate singles and doubles, a game limit of 1 will allow attendees to enter either Melee events or Smash Ultimate events, but not both.
Note: Not to confuse Events with Games, an Event would be the style tournament your players will be competing in. (For example: Smash 4 Singles, Melee Doubles, Tekken 1v1's, etc.)
Games, on the other hand. will be what your competitors are playing (For Example: Smash Ultimate, Melee, Tekken, etc.)