Attack quietly with little weight (6)
I believe the answer is:
pounce
'attack' is the definition.
(I've seen this before)
'quietly with little weight' is the wordplay.
'quietly' becomes 'p' (p for piano and quiet).
'with' says to put letters next to each other.
'little weight' becomes 'ounce' (unit of weight).
'p'+'ounce'='POUNCE'
(Other definitions for pounce that I've seen before include "Swoop down suddenly" , "Suddenly spring; fine powder" , "Spring down on and grasp" , "Jump or spring down as on prey" , "Spring upon suddenly" .)