Indicating ruler faced with ruin (7)
I believe the answer is:
marking
'indicating' is the definition.
(marking is a kind of indicating)
'ruler faced with ruin' is the wordplay.
'ruler' becomes 'king' (king is a kind of ruler).
'faced with' means one lot of letters go next to another.
'ruin' becomes 'mar' (I've seen this before).
'king' after 'mar' is 'MARKING'.
(Other definitions for marking that I've seen before include "Assessing script" , "Becoming stained" , "Staying close to an opposing player" , "Rating (school work)" , "assessment" .)