Union, or the other rugby (6)
I believe the answer is:
league
'union' is the definition.
(I know that league is a type of union)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for league that I've seen before include "Alliance, association" , "Alliance - three (poetic) miles" , "Combination of groups for a purpose, sports clubs perhaps" , "Former measure, approx. three miles" , "band together" .)