Backing last couple of actors in show (8)
I believe the answer is:
reversal
'backing last' is the definition.
'reversal' can be an answer for 'backing' (thesaurus). I am not sure about the 'last' bit.
'couple of actors in show' is the wordplay.
'couple of actors' becomes 'rs' (I can't explain this - if you can you should give a lot more credence to this answer).
'in' means one lot of letters goes inside another.
'show' becomes 'reveal' (revealing is a kind of showing).
'rs' going within 'reveal' is 'REVERSAL'.
Can you help me to learn more?
(Other definitions for reversal that I've seen before include "A change to an opposite direction" , "switch" , "A turning back" , "misfortune!" , "Negation" .)