Remove weapon from mad sir on the rampage (6)
I believe the answer is:
disarm
'remove weapon from' is the definition.
(I've seen this before)
'mad sir on the rampage' is the wordplay.
'on the rampage' indicates anagramming the letters.
'mad'+'sir'='madsir'
'madsir' is an anagram of 'DISARM'.
(Other definitions for disarm that I've seen before include "Give up weapons" , "Take weapons from or make less hostile" , "Mollify or remove weapon from" , "Pacify" , "Charm, win over" .)