One warning in four is shouted (4)
I believe the answer is:
fore
'one warning' is the definition.
(shouted in golf)
'four is shouted' is the wordplay.
'is shouted' indicates a 'sounds like' (homophone) clue (how the word might sound if shouted).
'four' sounds like 'FORE'.
'in' acts as a link.
(Other definitions for fore that I've seen before include "Warning cry on a golf course" , "At the bow" , "Placed in front" , "Not aft" , "Warning cry of golfer" .)