Nag, distressed, in perturbed condition, to stop moving (8)
I believe the answer is:
stagnate
'stop moving' is the definition.
(to stagnate is to stop developing or decline)
'nag distressed in perturbed condition' is the wordplay.
'distressed' is an anagram indicator.
'in' means one lot of letters goes inside another.
'perturbed condition' becomes 'state' (in a state).
'nag' anagrammed gives 'gna'.
'gna' placed into 'state' is 'STAGNATE'.
'to' acts as a link.
(Other definitions for stagnate that I've seen before include "Cease moving" , "Become still or stale through inactivity" , "turn foul" , "Cease motion" , "Become foul from inertia" .)