Happen to upset company dog (5)
I believe the answer is:
occur
'happen' is the definition.
(I know that happen is a more specific form of the action happen)
'upset company dog' is the wordplay.
'upset' is a reversal indicator.
'company' becomes 'co' (abbreviation).
'dog' becomes 'cur' (both can mean a despicable person).
'co' reversed gives 'oc'.
'oc'+'cur'='OCCUR'
'to' is the link.
(Other definitions for occur that I've seen before include "Happen - to come to mind" , "Happen, take place" , "Go on" , "appear" , "exist" .)