Institute legal proceedings against (3)
I believe the answer is:
sue
'institute legal proceedings against' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for sue that I've seen before include "Make a case against" , "- - Barker, 19 star" , "Bring a legal action" , "Appeal" , "The girl to take to court" .)