Theatre brought back organised groups with introduction of male shows (12)
I believe the answer is:
performances
'shows' is the definition.
(performance is a kind of show)
'theatre brought back organised groups with introduction of male' is the wordplay.
'theatre' becomes 'rep' (I've seen this before).
'brought back' is a reversal indicator.
'organised groups' becomes 'forces' (eg military forces).
'with introduction of' is an insertion indicator.
'male' becomes 'man' (man is a kind of male).
'rep' back-to-front is 'per'.
'forces' enclosing 'man' is 'formances'.
'per'+'formances'='PERFORMANCES'
(Another definition for performances that I've seen is " Operations".)