Is backtracking over David, for one, producing something fishy (6)
I believe the answer is:
scampi
'one producing something fishy' is the definition.
Although both the answer and definition are singular nouns, I don't understand how one could define the other.
'is backtracking over david' is the wordplay.
'backtracking' shows that the letters should be reversed in order.
'over' is an insertion indicator.
'david' becomes 'camp' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'is' in reverse letter order is 'si'.
'si' going around 'camp' is 'SCAMPI'.
'for' is the link.
Can you help me to learn more?
(Other definitions for scampi that I've seen before include "Large prawns cooked in batter" , "sort of seafood" , "Breaded prawns" , "Fish dish, often in rings" , "Fried seafood" .)