Concerned with diplomatic mission going down (10)
I believe the answer is:
relegation
'going down' is the definition.
The definition and answer can be both acts as well as being singular nouns.
Perhaps there's a link between them I don't understand?
'concerned with diplomatic mission' is the wordplay.
'concerned with' becomes 're' (re can mean regarding, concerning).
'diplomatic mission' becomes 'legation' (legation is a kind of diplomatic mission).
're'+'legation'='RELEGATION'
Can you help me to learn more?
(Other definitions for relegation that I've seen before include "Transference to a lower league" , "Demotion, to a lower league" , "that's going down" , "Lowering of status" .)