Hello, I understand (from what I read here for instance) the two main variants of rugby are named "rugby union" and "rugby league" in English. (We in France call it "rugby à 15" - that's union - ou "rugby à 13" depending on the number of players involved, so we generally ignore the union/league story no matter if we like these sports). I am a bit confused at the structure of these phrases: I think rugby is the main noun, modified by the word union (or league) which therefore acts a bit like an adjective. Then why isn't it "union rugby" and "league rugby" ? Does someone here have an idea how it works?