Writing in support of case of sabotage (5)
I believe the answer is:
prose
'writing' is the definition.
(I have seen 'Ordinary writing ' mean 'prose' so perhaps 'writing' could also mean 'prose')
'in support of case of sabotage' is the wordplay.
'in support of' becomes 'pro'.
'case of' says to hollow out the word (remove centre letters) (outsides of).
'sabotage' with its middle removed is 'se'.
'pro'+'se'='PROSE'
(Other definitions for prose that I've seen before include "Ropes (anag.)" , "Gossipy talker" , "Ordinary writing" , "Text" , "Normal written language" .)