Playing darts, lady is mean and wicked! (9)
I believe the answer is:
dastardly
'mean and wicked' is the definition.
(dastardly can mean villainous or cruel)
'playing darts lady' is the wordplay.
'playing' indicates anagramming the letters.
'darts'+'lady'='dartslady'
'dartslady' is an anagram of 'DASTARDLY'.
'is' acts as a link.
(Other definitions for dastardly that I've seen before include "Iniquitous" , "contemptible" , "Cruel" , "Cowardly" , "Despicable" .)