Wet coats left, muddy (6)
I believe the answer is:
sloppy
'muddy' is the definition.
(thesaurus)
'wet coats left' is the wordplay.
'wet' becomes 'soppy' (similar in meaning).
'coats' is an insertion indicator.
'left' becomes 'l' (common abbreviation).
'soppy' placed around 'l' is 'SLOPPY'.
(Other definitions for sloppy that I've seen before include "Runny" , "Slipshod" , "Romantic" , "Careless and messy" , "maudlin" .)