Giving up sitting in the auditorium (7)
I believe the answer is:
Here is my best explanation:
'giving up' is the definition.
'sitting in the auditorium' is the wordplay.
'sitting' becomes 'session' (eg a parliamentary session).
'in the auditorium' shows a homophone (sound like) (ie as heard on a stage).
'session' sounds like 'CESSION'.