Harry Potter's chair, where theatre's inferior players sit (9,3)
I believe the answer is:
orchestra pit
'where theatre's inferior players sit' is the definition.
(an orchestra pit is a sunken area below a stage)
'harry potter's chair' is the wordplay.
'harry' indicates anagramming the letters (I've seen this in other clues).
'potters'+'chair'='potterschair'
'potterschair' is an anagram of 'ORCHESTRA PIT'.
(Other definitions for orchestra pit that I've seen before include "Place for theatre musicians" , "Area in front of stage" , "where band plays" , "space for musicians" , "wind down in one" .)