Rugby Union gathering in the country (7)
I believe the answer is:
rurally
'in the country' is the definition.
(I've seen this before)
'rugby union gathering' is the wordplay.
'rugby union' becomes 'RU' (abbreviation).
'gathering' becomes 'rally' (rally is a kind of gathering).
'ru'+'rally'='RURALLY'
(Other definitions for rurally that I've seen before include "in the sticks?" , "country style" , "In the countryside" , "In country fashion" , "In a country manner" .)