Rugby game without wingers is flat (4)
I believe the answer is:
even
'is flat' is the definition.
(level)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for even that I've seen before include "Placid - not easily angered" , "neck and neck" , "Plumb" , "Going so far as to" , "Level, equal" .)