Black day after detective's put out of action (8)
I believe the answer is:
disabled
'put out of action' is the definition.
(I've seen this before)
'black day after detective's' is the wordplay.
'black' becomes 'sable' (heraldic term for black).
'day' becomes 'd' (abbreviation for day).
'after' says to put letters next to each other.
'detective' becomes 'di' (Detective Inspector abbreviation).
'sable'+'d'='sabled'
'sabled' after 'di' is 'DISABLED'.
(Other definitions for disabled that I've seen before include "Having a physical incapacity caused by injury or disease" , "Put out of action" , "Incapacitated" , "Not able to work" .)