Old theatre company picked up a stage work (5)
I believe the answer is:
opera
'stage work' is the definition.
(I've seen this before)
'old theatre company picked up a' is the wordplay.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'theatre company' becomes 'rep' (short for 'repertory theatre').
'picked up' is a reversal indicator.
'rep' back-to-front is 'per'.
'o'+'per'+'a'='OPERA'
(Other definitions for opera that I've seen before include "some theatrics" , "Musical piece accompanying a stage drama or comedy" , "Music and drama production" , "Eg, The Magic Flute" , "Norma is one" .)