Not what's usually done on leaving (9)
I believe the answer is:
departure
'leaving' is the definition.
(I know that leaving can be written as departure)
'not what's usually done on' is the wordplay.
I cannot quite see how this works, but
'done' could be 'u' and 'u' is located in the answer.
'on' could be 're' ('on' can be mean 'with reference to') and 're' is found in the answer.
The remaining letters 'depart' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for departure that I've seen before include "new approach" , "Exodus" , "Exit" , "shift" , "Not the usual" .)