In which one can winningly play to the gallery (4,6)
I believe the answer is:
real tennis
This could be a double definition.
'in which one can winningly' is the first definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
'play to the gallery' is the second definition.
Both the definition and answer are singular nouns.
I also know that 'play' relates to this answer.
(Other definitions for real tennis that I've seen before include "Game played in court" , "Early form of Wimbledon's game" , "In which court member served" , "ancient game" , "Old sport" .)