Black cat swagger (6)
I believe the answer is:
bounce
'swagger' is the definition.
(thesaurus)
'black cat' is the wordplay.
'black' becomes 'b' (as in pencil classifications).
'cat' becomes 'ounce' (ounce is a kind of cat).
'b'+'ounce'='BOUNCE'
(Other definitions for bounce that I've seen before include "Rebound (of ball)" , "Springiness" , "Showing self-confidence" , "Move energetically; rebound" , "Recoil like rubber ball" .)