Club, say, coming under pressure (6)
I believe the answer is:
putter
'club' is the definition.
(a golf club)
'say coming under pressure' is the wordplay.
'say' becomes 'utter' (to utter something is to speak or say it).
'coming under' says to put letters next to each other (in a down clue, some letters go below others).
'pressure' becomes 'p' (abbreviation).
'utter' put after 'p' is 'PUTTER'.
(Other definitions for putter that I've seen before include "Type of golf club" , "Golf-club" , "Golf club used on greens" , "Club to use on the green" , "Club used on the green" .)