Ensured observance of rules (8)
I believe the answer is:
enforced
'ensured observance of rules' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for enforced that I've seen before include "Corn feed (anag)" , "'Compelled observance of, a law say (8)'" , "Taken effect" , "Compulsory" , "Ensured observance of rules" .)