Reduction of power, say, is a must for hitting green targets (6)
I believe the answer is:
putter
'a must for hitting green targets' is the definition.
(needed for hitting targets on a golf green)
'reduction of power say' is the wordplay.
'reduction of' says to take the initial letters (the word is reduced to its first letter).
'say' becomes 'utter' (to utter something is to speak or say it).
The initial letter of 'power' is 'p'.
'p'+'utter'='PUTTER'
'is' acts as a link.
(Other definitions for putter that I've seen before include "Club used on the green" , "Golf club used on greens" , "Type of golf club" , "Club to use on the green" , "Golf-club" .)