Creating the event. Determining the time, place, structure, format, cost, etc.. This includes sanctioning the event.
Dealing with any problems on the day of the event (leaky roofs, not enough play space, not enough basic land, computer malfunctions, delays, etc.). Note: Some things will fall under the Head Judge's department (if you use a DCI Certified Judge), but if it's outside of game play, it's the Tournament Organizer’s responsibility.