Girls left with fools (6)
I believe the answer is:
lasses
'girls' is the definition.
(lass can mean a girl)
'left with fools' is the wordplay.
'left' becomes 'l' (common abbreviation).
'with' says to put letters next to each other.
'fools' becomes 'asses' (ass can mean a foolish person).
'l'+'asses'='LASSES'
(Other definitions for lasses that I've seen before include "Lads and - -" , "Young ladies" , "Northern girls?" .)