Operation for which you need the right backup (4)
I believe the answer is:
raid
'operation' is the definition.
(I know that raid is a type of incursion)
'the right backup' is the wordplay.
'the right' becomes 'r' (common abbreviation).
'backup' becomes 'aid' (backup is aid or assistance).
'r'+'aid'='RAID'
'for which you need' is the link.
(Other definitions for raid that I've seen before include "Go on the attack" , "bust" , "Sally" , "Surprise police visit" , "Maraud" .)