Spoils game in seconds (5)
I believe the answer is:
ruins
'spoils' is the definition.
(ruining is a kind of spoiling)
'game in seconds' is the wordplay.
'game' becomes 'ru' (rugby union).
'seconds' becomes 's'.
'ru'+'in'+'s'='RUINS'
(Other definitions for ruins that I've seen before include "Remains to be seen" , "Derelict buildings" , "dilapidated buildings" , "Damaged remains (of building)" , "Damages beyond repair" .)