Game, but not golf, in deep shade (4)
I believe the answer is:
ruby
'shade' is the definition.
(I have seen 'Shade of red' mean 'ruby' so perhaps 'shade' could also mean 'ruby')
'game but not golf in deep' is the wordplay.
I cannot really see how this works, but
'game' could be 'ru' (rugby union) and 'ru' is found in the answer.
The remaining letters 'by' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for ruby that I've seen before include "Girl's name - colour" , "Stony girl" , "Fortieth anniversary stone" , "Jack perhaps" , "killed an assassin" .)