Note:
The official spot is just next to the line (since the line is not part of the playing field), but a pivot foot on the line is also acceptable. Given the fact that perimeter lines are only a few centimetres wide, the "error" is too small to be significant. While the rules state that the pivot point should be established in-bounds, rule 11.3.2 also says that it is not a problem that the pivot foot contacts an out-of-bounds area. Extra: If the disc flew out the side of the end zone, there is a cone on the spot where the pivot point should be established. Rule 2.6 states that the edge of the central zone must be marked by that cone, so the player should not move it. Therefore the pivot point should be established on the end zone line next to the cone. Players should not move the cone. Note that the player is allowed to have enough room to turn on their pivot foot (otherwise unsafe situations might occur during pivoting).