Adults are moved behind black railing (10)
I believe the answer is:
Here is my best explanation:
'railing' is the definition.
(balustrade is a kind of railing)
'adults are moved behind black' is the subsidiary indication.
'moved' indicates anagramming the letters.
'behind' is a charade indicator (letters next to each other).
'black' becomes 'b' (abbreviation used in chess).
'adultsare' anagrammed gives 'alustrade'.
'alustrade' put after 'b' is 'balustrade'.
(Other definitions for balustrade that I've seen before include "Railing on stairs or balcony", "Railing at the side of a balcony", "Handrail", "Balcony railing", "Row of short pillars with coping", "Stair rail and its supports", "Railing supported on pillars", "Form of railing" and "Row of pillars under rail".)