Belt securing maiden's loose garment (5)
I believe the answer is:
smock
'loose garment' is the definition.
(type of loose-fitting garment)
'belt securing maiden's' is the wordplay.
'belt' becomes 'sock' (both can mean to hit).
'securing' indicates putting letters inside.
'maiden' becomes 'm' (cricket abbreviation).
'sock' placed around 'm' is 'SMOCK'.
(Other definitions for smock that I've seen before include "Loose dress or blouse" , "Artist's loose overall" , "Loose outer garment" , "artist's attire" , "Loose overall or dress" .)