Spoils things when one runs out (5)
I believe the answer is:
ruins
'spoils' is the definition.
(ruining is a kind of spoiling)
'when one runs out' is the wordplay.
'when one' becomes 'i' (Roman numeral. I am not sure about the 'when' bit.).
'out' is an insertion indicator.
'i' inserted inside 'runs' is 'RUINS'.
'things' is the link.
Can you help me to learn more?
(Other definitions for ruins that I've seen before include "Wrecked buildings" , "Damaged remains (of building)" , "Broken-down remnants" , "dilapidated buildings" , "Damages beyond repair" .)