Away goal causes upset (6)
I believe the answer is:
offend
'upset' is the definition.
(offend can mean to upset or insult)
'away goal' is the wordplay.
'away' becomes 'off' (synonyms).
'goal' becomes 'end' (both can mean a purpose).
'off'+'end'='OFFEND'
'causes' is the link.
(Other definitions for offend that I've seen before include "disgust" , "Distress" , "Cause displeasure or hurt, be nasty towards" , "Commit an illegal act" , "Act in disregard of the law" .)