to help shed some light on possible options for the celtics, here is part of the thread on the topic over at SoSH:
A hardship exemption means clearing a fairly high hurdle. A team can apply to the NBA Board of Governors for an additional roster spot, but it can get one automatically if at least four players on the roster to be injured or ill:
In the event that a Member [read "team"--GM49] has three (3) Players on its Active List and/or Inactive List who are unable to perform playing services due to injury or illness and such Member has an additional Player who becomes unable to perform playing services due to injury or illness, it may substitute a Player in his stead after the following has occurred:
(a) each of the three (3) injured or ill Players and the additional injured or ill Player has missed a minimum of three (3) consecutive games due to injury or illness; and
(b) the Commissioner’s Office has determined, through an independent physician, if necessary, that at the time the replacement Player is signed, each of the three (3) injured or ill Players on the Member’s Active and/or Inactive List, and the additional injured or ill Player, will continue to be unable to perform playing services due to injury or illness.
So, Hayward, Theis, and Smart would certainly qualify as the three injured or ill players, and Brown would count as the fourth if he needed to be out for an extended period of time.
http://sonsofsamhorn.net/index.php?threads/smart-out-indefinitely-with-torn-thumb-tendon.22640/#post-2703842