Male in rotten mess causes pain (7)
I believe the answer is:
torment
'pain' is the definition.
(I know that torment is a kind of pain)
'male in rotten mess' is the wordplay.
'male' becomes 'm' (common abbreviation).
'in' is an insertion indicator.
'mess' indicates anagramming the letters.
'rotten' is an anagram of 'torent'.
'm' put into 'torent' is 'TORMENT'.
'causes' is the link.
(Other definitions for torment that I've seen before include "Harass" , "Severe physical or mental suffering" , "Persecute" , "Tease unkindly" , "More TNT (anag.)" .)