Mischievous troublemaker (7)
I believe the answer is:
gremlin
'mischievous troublemaker' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for gremlin that I've seen before include "cause of trouble for airmen" , "Mischievous troublemaker" , "One sabotages" , "Mechanical mischief-maker" , "Imp bedevilling plane" .)