Cards for winning service (4)
I believe the answer is:
aces
This might be a double definition.
'cards for winning' is the first definition.
'aces' can be an answer for 'cards' (I have seen 'Top cards' mean 'aces' so perhaps 'cards' could also mean 'aces'). I am not sure about the 'for winning' bit.
'service' is the second definition.
(I have seen 'excellent service' mean 'aces' so perhaps 'service' could also mean 'aces')
Can you help me to learn more?
(Other definitions for aces that I've seen before include "Winning serves" , "Flying war heroes" , "Top cards or people" , "Tennis serves the receiver can't reach" , "Experts (in their field)" .)