Troops drop GI, taking odds for leader (3,3)
I believe the answer is:
top dog
'leader' is the definition.
(I know that top dog is a type of leader)
'troops drop gi taking odds' is the wordplay.
'taking odds' means one should take alternating letters (only letters in odd-numbered positions).
'troops'+'drop'+'gi'='troopsdropgi'
The alternating letters of 'troopsdropgi' are 'TOP DOG'.
'for' acts as a link.
(Other definitions for top dog that I've seen before include "Informally, the master or victor" , "Crufts champion" , "One pre-eminent in their field" , "Master or victor of canine hue" , "high in the sky?" .)