Negative! I'd be in back for Norse god (4)
I believe the answer is:
odin
'norse god' is the definition.
(Odin is an example)
'negative i'd be in back' is the wordplay.
'negative' becomes 'no' (no is a kind of negative).
'be in' indicates putting letters inside.
'back' shows that the letters should be reversed in order.
'no' placed around 'id' is 'nido'.
'nido' written backwards gives 'ODIN'.
'for' is the link.
(Other definitions for odin that I've seen before include "Scandinavian war god" , "Mythological Norse god of war" , "Pagan god" , "Legendary Scandinavian" , "Chief Norse god" .)