Troubled hunter battles to get the upper hand (4,3,6)
I believe the answer is:
turn the tables
'get the upper hand' is the definition.
'troubled hunter battles' is the wordplay.
'troubled' is an anagram indicator.
'hunter'+'battles'='hunterbattles'
'hunterbattles' with letters rearranged gives 'TURN THE TABLES'.
'to' is the link.
(Other definitions for turn the tables that I've seen before include "Reverse fortune" , "Cause a reversal of fortune" , "Change from losing to winning" , "Gain an advantage from an unfavourable position" , "Reverse the positions" .)