Stage yet to be erected, back to front (3,2)
I believe the answer is:
put on
'stage' is the definition.
(as in putting on a show)
'yet to be erected back to front' is the wordplay.
I cannot really see how this works, but
'to' is within the answer.
The remaining letters 'pun' is a valid word which might be clued in a way I don't see.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for put on that I've seen before include "Increase as with weight" , "in an unnatural way" , "Stage -- hoax" , "Apply (to a surface) - present (on stage)" , "Donned" .)