Pastoral sport advanced when embraced by both sides (5)
I believe the answer is:
rural
'pastoral' is the definition.
(I know that pastoral can be written as rural)
'sport advanced when embraced by both sides' is the wordplay.
'sport' becomes 'RU' (rugby union).
'advanced' becomes 'a' (abbreviation).
'when embraced by' means one lot of letters goes inside another.
'both sides' becomes 'RL' (abbreviation for left and right).
'a' placed within 'rl' is 'ral'.
'ru'+'ral'='RURAL'
(Other definitions for rural that I've seen before include "Relating to the countryside" , "Arcadian" , "Not urban" , "Characteristic of the countryside" , "Connected with farming" .)