Last bit of bad fruit spot (6)
I believe the answer is:
dapple
'spot' is the definition.
(dappling is a kind of spotting)
'last bit of bad fruit' is the wordplay.
'last bit of' says to take the final letters.
'fruit' becomes 'apple' (apple is a kind of fruit).
The final letter of 'bad' is 'd'.
'd'+'apple'='DAPPLE'
(Other definitions for dapple that I've seen before include "Mottle" , "Mark with coloured spots; such a horse" , "Spotted" , "Mark(ed) with spots" , "Patch of colour or light" .)