A witness has told South Australia's Supreme Court he saw two men arguing with his friend shortly before his friend was allegedly bashed, leading to his death.
Sam Davis, 17, died after allegedly being hit at a Brighton party in May 2008.
Heath Arthur Clake, 19, has pleaded not guilty to Davis' manslaughter.
Davis' friend, Jack Leroy Symonds, testified he attended the party where he was punched and put in a headlock by a man wearing a black jacket.
He said he later saw the same man and another person arguing with Davis in front of the party house.
Symonds said he went to intervene but was hit by the other person.
When he looked back towards Davis he saw his friend lying on the ground and the two men were gone.