Destructive person causing flap (7)
I believe the answer is:
spoiler
This clue is a double definition.
'destructive person' is the first definition.
(I've seen this before)
'flap' is the second definition.
(I've seen this before)
'causing' acts as a link.
(Other definitions for spoiler that I've seen before include "Flap putting brake on" , "attachment to racing car" , "News story published to ruin another" , "Sore lip (anag.)" , "Part of a racing car" .)