Demanding individual, possibly sour (7)
I believe the answer is:
onerous
'demanding' is the definition.
(thesaurus)
'individual possibly sour' is the wordplay.
'individual' becomes 'one' (**).
'possibly' indicates an anagram.
'sour' is an anagram of 'rous'.
'one'+'rous'='ONEROUS'
(Other definitions for onerous that I've seen before include "Challenging" , "Burdensome, heavy kind of duty" , "Involving much effort" , "Involving much work" , "Burdensome as duty may be" .)