Striped yellow balls, in pool
I believe the answer is:
'striped yellow balls in pool' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for nines that I've seen before include "Dressed to these is to be perfectly turned out" , "9s" , "Numbers to which one may be dressed up?" , "In emergency, press three of these" , "Dressed to these and you're well-turned-out" .)