Operative and I cover obstacle (8)
I believe the answer is:
handicap
'obstacle' is the definition.
(thesaurus)
'operative and i cover' is the wordplay.
'operative' becomes 'hand' (I've seen this in other clues).
'and' is a charade indicator (letters next to each other).
'cover' becomes 'cap' (cap is a kind of cover**).
'hand'+'i'+'cap'='HANDICAP'
(Other definitions for handicap that I've seen before include "Grand National for example" , "Limit" , "advantage - or the opposite" , "Advantage given to equalise chances of winning" , "liability" .)