Shots from above hit destroyer's bow — lost about six, not nine (4,5)

'shots from above' is the definition.
(basketball shots)

'hit destroyer's bow lost about six not nine' is the wordplay.
I cannot quite understand how this works, but
'hit' could be 'slam' (slamming is a kind of hitting) and 'slam' is located in the answer.
'not' could be 'un' (prefix meaning 'not') and 'un' is found in the answer.
This explanation may well be incorrect...