Preempted, as a sitcom (3,2)
I believe the answer is:
not on
'preempted as a sitcom' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for not on that I've seen before include "Definitely inadvisable" , "Informally, can't be accepted or tolerated" , "Out of the question" , "Modern phrase for unacceptable" , "Informally, cannot be permitted or tolerated" .)