"Not guilty,” for one (4)
I believe the answer is:
plea
'not guilty for one' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for plea that I've seen before include "suit" , "Urgent request" , "Leap (anag.)" , "(and 14) Enjoyment - gratification" , "Defence - excuse - appeal" .)