Rare slip somehow results in act of retaliation (8)
I believe the answer is:
reprisal
'act of retaliation' is the definition.
(I've seen this before)
'rare slip somehow' is the wordplay.
'somehow' is an anagram indicator.
'rare'+'slip'='rareslip'
'rareslip' with letters rearranged gives 'REPRISAL'.
'results in' is the link.
(Other definitions for reprisal that I've seen before include "Retaliatory deed" , "Retaliation for an injury" , "comeback" , "revenge attack" , "hitting back" .)