Right to help in sudden attack (4)
I believe the answer is:
raid
'sudden attack' is the definition.
(I've seen this in another clue)
'right to help' is the wordplay.
'right' becomes 'r' (common abbreviation).
'to help' becomes 'aid' ('aid' can be a synonym of 'help').
'r'+'aid'='RAID'
'in' acts as a link.
(Other definitions for raid that I've seen before include "bust" , "military operation" , "Rifle" , "Search by police without warning" , "Enter a territory and take spoils" .)