Left expert some material (4)
I believe the answer is:
lace
'some material' is the definition.
(lace is a kind of material)
'left expert' is the wordplay.
'left' becomes 'l' (common abbreviation).
'expert' becomes 'ace' (ace can informally mean very good).
'l'+'ace'='LACE'
(Other definitions for lace that I've seen before include "Delicate open-web fabric" , "Fine needlework" , "Shoe tie" , "Fabric made in openwork design" , "Fortify with spirits; open fabric" .)