Quiet snow leopard to attack as cats do (6)
I believe the answer is:
pounce
'attack as cats do' is the definition.
(to pounce on someone is to attack them)
'quiet snow leopard' is the wordplay.
'quiet' becomes 'p' (music symbol for 'piano', ie soft or quiet).
'snow leopard' becomes 'ounce' (ounce is an alternative name for the snow leopard).
'p'+'ounce'='POUNCE'
'to' acts as a link.
(Other definitions for pounce that I've seen before include "Spring or swoop down on to attack" , "Jump swiftly on, as cat might" , "Jump down on suddenly" , "Act fast to take advantage" , "Jump or spring down as on prey" .)