Jet hit by martial arts expert (5,4)
I believe the answer is:
black belt
'martial arts expert' is the definition.
(I've seen this before)
'jet hit' is the wordplay.
'jet' becomes 'black' (similar in meaning).
'hit' becomes 'belt' (belting is a kind of hitting).
'black'+'belt'='BLACK BELT'
'by' acts as a link.
(Other definitions for black belt that I've seen before include "Expert in a martial art" , "It's worn by a Karate expert" , "Combat ace" , "Martial arts expert" , "Rank in the martial arts" .)