A golfer won't take it lying down (6)
I believe the answer is:
stance
'lying down' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.
'a golfer won't take it' is the wordplay.
I cannot really understand how this works, but
'a' could be 'an' and 'an' is found within the answer.
'it' could be 't' (abbreviation. e.g. in 'tis) and 't' is found within the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for stance that I've seen before include "Position assumed by upright person" , "Way of standing, like golfer addressing ball" , "Standpoint" , "policy" , "One's physical or mental attitude" .)