Uncouth philosopher losing heart after game (6)
I believe the answer is:
rustic
'uncouth' is the definition.
(rustic can uncouth or unrefined)
'philosopher losing heart after game' is the wordplay.
'philosopher' becomes 'Stoic' (type of ancient philosopher).
'losing heart' suggests removing the centre.
'after' says to put letters next to each other.
'game' becomes 'RU' (rugby union).
'stoic' with its centre taken out is 'stic'.
'stic' after 'ru' is 'RUSTIC'.
(Other definitions for rustic that I've seen before include "Of the countryside and country folk" , "plain" , "Rural, country" , "Citrus (anag)" , "Quaintly countrified" .)