Incident some prevented (5)
I believe the answer is:
event
'incident' is the definition.
(an incident is an event or happening)
'some prevented' is the wordplay.
'some' indicates a hidden word (some of the parts of the word are used).
'EVENT' is hidden in the letters of 'prevented'.
(Other definitions for event that I've seen before include "Something that takes place" , "major incident" , "Incident - final outcome" , "Occurence, occasion" , "Occurren" .)