Post to get stuck in the auditorium (4)
I believe the answer is:
jamb
'post' is the definition.
(thesaurus)
'get stuck in the auditorium' is the wordplay.
'get stuck' becomes 'jam' ('jam' can be a synonym of 'get stuck').
'in the auditorium' indicates a 'sounds like' (homophone) clue (ie as heard on a stage).
'jam' is a homophone of 'JAMB'.
'to' acts as a link.
(Other definitions for jamb that I've seen before include "Door sidepiece" , "Side post of a doorway" , "Side of door frame" , "Upright sidepiece" , "part of doorway?" .)