Hanger-on right to stop balance being disturbed (8)
I believe the answer is:
barnacle
'hanger-on' is the definition.
(I've seen this before)
'right to stop balance being disturbed' is the wordplay.
'right' becomes 'r' (common abbreviation).
'to stop' indicates putting letters inside (stopping can mean blocking a gap).
'being disturbed' is an anagram indicator (the order of letters is disturbed).
'balance' anagrammed gives 'banacle'.
'r' put inside 'banacle' is 'BARNACLE'.
(Other definitions for barnacle that I've seen before include "hanger-on" , "Crustacean that attaches to a submerged surface" , "A shellfish that sticks to objects under water" , "underwater attachment" , "Crustacean that attaches to submerged surfaces" .)