Seizes wrongfully (6)
I believe the answer is:
usurps
'seizes wrongfully' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for usurps that I've seen before include "Seizes and takes control without authority" , "Takes a position of power illegally" , "Seizes wrongfully or by force" , "Arrogates" , "Takes position wrongfully or by force" .)