Leftovers on retiring is expected (7)
I believe the answer is:
residue
'leftovers' is the definition.
(I've seen this in another clue)
'on retiring is expected' is the wordplay.
'on' becomes 're' ('on' can be mean 'with reference to').
'retiring' shows that the letters should be reversed in order.
'expected' becomes 'due' (similar in meaning).
'is' reversed gives 'si'.
're'+'si'+'due'='RESIDUE'
(Other definitions for residue that I've seen before include "It remains after other parts have been taken away" , "Surplus" , "Small amount remaining" , "rest" , "Whatever is left over" .)