Fish for the backward kid (3)
I believe the answer is:
gar
'fish' is the definition.
(type of gar)
'backward kid' is the wordplay.
'backward' shows that the letters should be reversed in order.
'kid' becomes 'rag' (I've seen this in other clues).
'rag' back-to-front is 'GAR'.
'for the' acts as a link.
(Other definitions for gar that I've seen before include "swimmer" , "Pike-like fish" , "Creature" , "A fish; cloth scrap (reversed)" , "Type of fish" .)