Foremost of prizes, say, in golf club (6)
I believe the answer is:
putter
'golf club' is the definition.
(type of golf club)
'foremost of prizes say' is the wordplay.
'foremost of' suggests taking the first letters.
'say' becomes 'utter' (to utter something is to speak or say it).
The first letter of 'prizes' is 'p'.
'p'+'utter'='PUTTER'
'in' acts as a link.
(Other definitions for putter that I've seen before include "Club to use on the green" , "Club used on the green" , "Golf club used on greens" , "Golf-club" , "Type of golf club" .)