A theatre, set up in support of ordinary theatrical production (5)
I believe the answer is:
opera
'theatrical production' is the definition.
'opera' can be an answer for 'production' (thesaurus). I am not sure about the 'theatrical' bit.
'a theatre set up in support of ordinary' is the wordplay.
'theatre' becomes 'rep' (I've seen this in other clues**).
'set up' says the letters should be written in reverse.
'in support of' says to put letters next to each other (I've seen this in other clues).
'ordinary' becomes 'o' (abbreviation e.g. O-Levels).
'a'+'rep'='arep'
'arep' written backwards gives 'pera'.
'pera' after 'o' is 'OPERA'.
Can you help me to learn more?
(Other definitions for opera that I've seen before include "Glyndebourne production" , "Grand or comic work?" , "Macbeth, say" , "Eg, Rigoletto" , "La Scala production, perhaps" .)