Oil patch spread around a banger (9)
I believe the answer is:
chipolata
'banger' is the definition.
(I've seen this before)
'oil patch spread around a' is the wordplay.
'spread around' indicates anagramming the letters.
'oil'+'patch'='oilpatch'
'oilpatch' anagrammed gives 'chipolat'.
'chipolat'+'a'='CHIPOLATA'
(Other definitions for chipolata that I've seen before include "Type of sausage" , "Party snack" , "banger" , "Small thin sausage" .)