Never do move Derby Day, somehow (4,2,4,4)
I believe the answer is:
over my dead body
'never' is the definition.
(I've seen this before)
'do move derby day somehow' is the wordplay.
'somehow' indicates anagramming the letters.
'do'+'move'+'derby'+'day'='domovederbyday'
'domovederbyday' is an anagram of 'OVER MY DEAD BODY'.
(Other definitions for over my dead body that I've seen before include "not if I have any say" , "Where six feet of earth shovelled" , "Not if I can help it!" , "No way" , "Where earth may be scattered" .)