Rubbish left by old earth excavator (5)
I believe the answer is:
offal
'rubbish' is the definition.
(I've seen this in another clue)
'left by old earth excavator' is the wordplay.
'left' becomes 'al' (I've seen this in other clues).
'by' is a charade indicator (letters next to each other).
'old earth excavator' becomes 'off' (I am not sure about this - if you are sure you should believe this answer much more).
'al' after 'off' is 'OFFAL'.
Can you help me to learn more?
(Other definitions for offal that I've seen before include "Internal organs and entrails as food" , "Tripe, sweetbreads" , "Entrails used as food" , "Less edible parts of animal, entrails and organs" , "Edible innards" .)