Quantity noticed around incident (9)
I believe the answer is:
seventeen
'quantity' is the definition.
(seventeen is a kind of quantity)
'noticed around incident' is the wordplay.
'noticed' becomes 'seen' (I've seen this before).
'around' is an insertion indicator.
'incident' becomes 'event' (I've seen this before).
'seen' enclosing 'event' is 'SEVENTEEN'.
(Other definitions for seventeen that I've seen before include "Figure" , "Cardinal number" , "odd number" , "Quite a few" , "XVII" .)