Hang cage over top of door (4)
I believe the answer is:
pend
'hang' is the definition.
(I've seen this before)
'cage over top of door' is the wordplay.
'cage' becomes 'pen' (I've seen this in another clue).
'over' is a charade indicator (letters next to each other).
'top of' suggests taking the first letters.
The initial letter of 'door' is 'd'.
'pen'+'d'='PEND'
(Other definitions for pend that I've seen before include "Hang, as in a balance" , "Loom" , "Hang; remain undecided" .)