Oppose a refractory mob act (6)
I believe the answer is:
combat
'oppose' is the definition.
(I've seen this before)
'a refractory mob act' is the wordplay.
'a refractory' is an anagram indicator.
'mob'+'act'='mobact'
'mobact' anagrammed gives 'COMBAT'.
(Other definitions for combat that I've seen before include "Oppose" , "Fight against; fighting" , "sort of jacket" , "War; contest" , "Military fighting" .)