Stopped king interrupting a challenge (2,4)
I believe the answer is:
at rest
'stopped' is the definition.
(I've seen this before)
'king interrupting a challenge' is the wordplay.
'king' becomes 'r' (r is abbreviation for rex).
'interrupting' indicates putting letters inside.
'challenge' becomes 'test'.
'a'+'test'='atest'
'r' placed into 'atest' is 'AT REST'.
(Other definitions for at rest that I've seen before include "Motionless" , "Immobile" , "Not moving, free from trouble - maybe dead" , "calm" , "Free from trouble or anxiety" .)