Reposition bad sign in middle (7)
I believe the answer is:
abdomen
'middle' is the definition.
(I've seen this in another clue)
'reposition bad sign' is the wordplay.
'reposition' is an anagram indicator (I've seen 'repositioned' mean this).
'sign' becomes 'omen' (omen is a kind of sign).
'bad' is an anagram of 'abd'.
'abd'+'omen'='ABDOMEN'
'in' acts as a link.
(Other definitions for abdomen that I've seen before include "Where one digests" , "Midriff" , "Central region" , "A main part of the body" , "gut" .)