At a PDGA sanctioned event, teeing off rules state that you must tee from the provided tee with all supporting points on the tee upon release of the disc. If a natural tee is used (grass/dirt) with flags or a line painted, you can take up to 3 meters straight back.
803.02A: Play shall begin on each hole with the player throwing from within the teeing area. When the disc is released, at least one of the player's supporting points must be in contact with the surface of the teeing area, and all the player's supporting points must be within the teeing area. If a tee pad is provided, all supporting points must be on the pad at the time of release, unless the director has specified a modified teeing area for safety reasons. If no tee pad is provided, all supporting points at the time of release must be within an area encompassed by the front line of the teeing area and two lines perpendicular to and extending back three meters from each end of the front line. The front line of the teeing area includes the outside edges of the two tee markers. Running up from behind the teeing area before the disc is released is permitted. Following through in front of the teeing area is permitted provided there is no supporting point contact outside the teeing area when the disc is released.
B. Any supporting point contact outside the teeing area at the time of release constitutes a stance violation and shall be handled in accordance with sections 803.04 F, G and H.