A foe nervously tucking into some ground fish, say (7)
I believe the answer is:
seafood
'fish say' is the definition.
(fish is a kind of seafood)
'a foe nervously tucking into some ground' is the wordplay.
'nervously' indicates an anagram.
'tucking into' indicates putting letters inside.
'some ground' becomes 'sod' (both can mean a piece of earth).
'a'+'foe'='afoe'
'afoe' is an anagram of 'eafo'.
'eafo' put inside 'sod' is 'SEAFOOD'.
(Other definitions for seafood that I've seen before include "Such as prawns, tuna" , "Eaten fish and shellfish" , "The "surf" of a surf 'n' turf dish" , "Shellfish, marine fish" , "Edible fish, shellfish etc from the oceans" .)