The Basketball is one of the rarest miscellaneous items in the Thief Universe and can only be found in the secret basketball court inside the Keeper Compound in the Thief: The Dark Project/Thief Gold mission "A Keeper's Training" (along with a Bedroll containing a list of Quotes from the Dark Team). The object itself has the appearance of a normal orange basketball, and is the only known object in the first two games with the ability to bounce up from the ground.
Accessing the Basketball Court[]
Access to this room is only possible for a brief period on Expert difficulty, during the sparring match or shortly afterwards, when the Sparring Partner is leaving the courtyard. The portcullis on the doorway will not close unless Garrett is out in the courtyard, so the room on the other side can be entered by following closely after the Sparring Partner. This room is connected to the basketball court by a corridor with a locked wooden door which can be opened with the key from the courtyard table, or simply bashed open using the sword. Note, however, that on Normal and Hard difficulty the path is blocked by an immovable stone wall.