Overhand

From Ultipedia

To grip the disc, place the side of you thumb on the inside edge of the disc, your index finger along the outside of the disc, and your remaining three fingers on top of the disc. You release the throw at or above shoulder height on the forehand side. To begin the throw, grip the disc then hold it upside-down at your waist. Loop your arm behind your back forming a C then snap your wrist and realease with the outside edge slightly down.