Made a mess of the cod, awfully black on top (7)
I believe the answer is:
botched
'made a mess of' is the definition.
(I've seen this in another clue)
'the cod awfully black on top' is the wordplay.
'awfully' indicates an anagram.
'black' becomes 'b' (as in pencil classifications).
'on top' means one lot of letters go next to another (in a down clue, some letters go above others).
'the'+'cod'='thecod'
'thecod' is an anagram of 'otched'.
'otched' put after 'b' is 'BOTCHED'.
(Other definitions for botched that I've seen before include "Made a mess of, spoiled by clumsy work" , "Made a bags of" , "Messed up" .)