Become suddenly aggressive, as Whip is not in The House (4,3)
I believe the answer is:
lash out
'become suddenly aggressive' is the definition.
(I've seen this before)
'whip is not in the house' is the wordplay.
'whip' becomes 'lash' ('lash' can be a synonym of 'whip').
'is not in the house' becomes 'out' (I can't justify this - if you can you should give a lot more credence to this answer).
'lash'+'out'='LASH OUT'
'as' is the link.
(Other definitions for lash out that I've seen before include "React violently" , "unprovoked attack" , "Attack with blows or words - using whip?" , "Attack, verbally or physically" , "spend a fortune" .)