Behave theatrically, breaking top off TV control (5)
I believe the answer is:
emote
'behave theatrically' is the definition.
(to emote is to display emotion)
'breaking top off tv control' is the wordplay.
'breaking top off' means to remove the first letter.
'tv control' becomes 'remote' (I've seen this before).
'remote' with its initial letter taken off is 'EMOTE'.
(Other definitions for emote that I've seen before include "Display strong feeling in a theatrical manner" , "Express strong feeling" , "Show feeling excessively" , "Behave theatrically" , "Express exaggerated feelings" .)