A man told a court he was defending himself when he kicked a homeless alcoholic.
Joe Budgen said that Matthew Heading, described as dressing "like Rambo", was known to carry a knife.
Mr Heading, 41, died from a ruptured spleen two days after he was attacked outside the Brighton hostel he stayed at.
It is alleged he was kicked and stamped on in the attack in Grand Parade last June 21. It followed an incident in a mobile phone shop in London Road involving Budgen's pregnant sister.
Mr Heading and his friend Joe Burton were allegedly confronted outside the hostel by Budgen, Oliver McNulty, Adam Todd and Paul Hamlet.
Christine Laing QC, prosecuting, said all four either took part in the attack or encouraged the others to do so.
Budgen denies stamping on Mr Heading but said he shoved him in the back with his foot and he fell over.
The defendant said he had seen Mr Heading with a knife before and believed he had a reputation for carrying one.
He said he heard Mr Heading say "I will get my knife" after Todd had punched Mr Burton.
And he told Hove Crown Court McNulty had put a hand on his shoulder and jumped in the air, landing on Mr Heading's head.
Court witness Catherine Back said Mr Heading had been a familiar sight in the area, dressed "like Rambo" in a camouflage jacket, and was often drunk and aggressive.
She said police had been called to an incident near her home in New England Street in October 2005 when he had threatened a boy of about eight with a knife.
McNulty, 18, of New England Street, Brighton, Budgen, 19, of Ann Street, Brighton, Todd, 25, of Ropetackle Walk, Shoreham, and Hamlet, 32, of Falcon Court, Whitehawk, Brighton, all deny murder.
They also deny causing actual bodily harm to Mr Burton. The trial continues.
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