Expert wearing a new protective garment (5)
I believe the answer is:
apron
'protective garment' is the definition.
(apron is a kind of protective garment)
'expert wearing a new' is the wordplay.
'expert' becomes 'pro' (I've seen this before).
'wearing' is an insertion indicator.
'a new' becomes 'an' (I've seen this in other clues).
'pro' placed into 'an' is 'APRON'.
(Other definitions for apron that I've seen before include "Area for aircraft not in use" , "Pinnie" , "Protective garment - part of stage" , "item of clothing in the kitchen" , "Part of stage in front of the curtain" .)