During audition, Mark traps instrument (6)
I believe the answer is:
cymbal
'instrument' is the definition.
(cymbal is a kind of instrument)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for cymbal that I've seen before include "Origin of the Clash" , "One of a pair of brass musical instruments" , "Musical instrument (no use by itself!)" , "Percussion instrument like brass plate" , "One of a pair of percussion instruments" .)