Break up to join the cast, perhaps (4,5)
I believe the answer is:
take apart
'break up' is the definition.
(I know that break up can be written as take apart)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for take apart that I've seen before include "Severely criticise" , "Dismantle - act in drama 4,1,4" , "roast" , "Disassemble" , "Strip" .)