Game at home results in defeat (4)
I believe the answer is:
ruin
'defeat' is the definition.
(I've seen this before)
'game at home' is the wordplay.
'game' becomes 'ru' (rugby union).
'at home' becomes 'in' ('in' can be similar in meaning to 'at home').
'ru'+'in'='RUIN'
'results in' acts as a link.
(Other definitions for ruin that I've seen before include "Wreck" , "Destruction or bankruptcy" , "loss of position" , "Physical collapse" , "building now demolished" .)