Go mad, following insolence (4)
I believe the answer is:
flip
'go mad' is the definition.
(to flip is to become very angry suddenly)
'following insolence' is the wordplay.
'following' becomes 'f' (used when citing page numbers etc).
'insolence' becomes 'lip' (I've seen this before).
'f'+'lip'='FLIP'
(Other definitions for flip that I've seen before include "hit the roof" , "Lose one's cool - reverse side" , "Toss e.g. a coin" , "Propel with finger - lose one's temper" , "B-side" .)