Ann Arbor Ultimate Forum

http://upa.org/ultimate/rules/11th#IX

# In- and Out-of-bounds

   1. The entire playing field is in-bounds. The perimeter lines are not part of the playing field and are out-of-bounds.
   2. The out-of-bounds area consists of the ground which is not in-bounds and everything in contact (direct or indirect) with it except for players. Any non-players other than observers are considered part of the out-of-bounds area.
   3. A player contacting the out-of-bounds area is out-of-bounds. A player who is not out-of-bounds is in-bounds. An airborne player retains in-bounds or out-of-bounds status until that player contacts the playing field or the out-of-bounds area. The following exceptions apply:
         1. If momentum carries a player out-of-bounds after landing in-bounds with possession of an in-bounds disc, the player is considered in-bounds. For this exception to apply, that player’s first point of ground contact with any area must be completely in-bounds. The disc is put into play at the spot on the perimeter line of the playing field where the player first went out-of-bounds (unless X.A.2 applies). If the player traversed the end zone being attacked, XI.B applies.

I would like to add, if the person catching the disk dosn't know if they are in or out of bounds the call go's to a person with the best perspective view of the play.