noun
rugby union
Refers specifically to the 15-a-side code of rugby, as opposed to rugby league (ラグビーリーグ) or sevens (7人制ラグビー).
ラグビーユニオンは15人制で行われます。
Rugby union is played with 15 players per side.
彼は高校からラグビーユニオンを始めた。
He started playing rugby union in high school.