Difficult rabble not totally extreme (5)
I believe the answer is:
ultra
'extreme' is the definition.
(I've seen this before)
'difficult rabble not totally' is the wordplay.
'not totally' says the answer is hidden in the clue (only some letters are used).
'ULTRA' is hidden within 'difficult rabble'.
(Other definitions for ultra that I've seen before include "Prefix meaning beyond or extremely" , "Person holding extreme views" , "(As prefix) beyond or extreme" , "such sound treatment?" , "Secret intelligence" .)