Grievance expressed when one enters place (6)
I believe the answer is:
plaint
'grievance expressed' is the definition.
(accusation brought forth by a plaintiff)
'one enters place' is the wordplay.
I cannot really see how this works, but
'one' could be 'i' (Roman numeral) and 'i' is found within the answer.
'place' could be 'plant' (planting is a kind of placing) and 'plant' is present in the remaining letters.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
'when' is the link.
(Other definitions for plaint that I've seen before include "Mournful song" , "Lamentation; charge (law)" , "statement of grievance" , "Cry of sorrow or grief" , "Archaic word for grievance (6)" .)