Happen to see the ball caught by the dog (5)
I believe the answer is:
occur
'happen' is the definition.
(I know that happen can be written as occur)
'the ball caught by the dog' is the wordplay.
'the ball' becomes 'o' (letter resembling a ball).
'caught' becomes 'c' (cricket abbreviation).
'by' is a charade indicator (letters next to each other).
'the dog' becomes 'cur' (both can mean a despicable person).
'o'+'c'+'cur'='OCCUR'
'to see' is the link.
(Other definitions for occur that I've seen before include "crop up" , "found" , "Happen - to come to mind" , "exist" , "Go on" .)