Black cat's leap (6)
I believe the answer is:
bounce
'leap' is the definition.
(bouncing is a kind of leaping)
'black cat's' 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 (like a cheque)" , "Throw out" , "Hop like rubber ball" , "Rebound (of ball)" , "Spring back; resilience" .)