A sporting warning, of course (4)

I believe the answer is:

fore

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'warning of course' is the definition.
(used to warn of airborne balls on a golf course)

I can't explain the rest of the clue.

Can you help me to learn more?

(Other definitions for fore that I've seen before include "Placed in front" , "Warning cry of golfer" , "Not aft" , "Ancestor" , "Word of warning to golfers" .)

I've seen this clue in the Evening Standard.

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