Go berserk: hit boy attendant (7)
I believe the answer is:
rampage
'go berserk' is the definition.
(I've seen this before)
'hit boy attendant' is the wordplay.
'hit' becomes 'ram' (ram can mean to hit something).
'boy attendant' becomes 'page' (I've seen this before).
'ram'+'page'='RAMPAGE'
(Other definitions for rampage that I've seen before include "Violent action" , "Run wild" , "Violent disorder" , "A mad rush" , "Map gear (anag.)" .)