Cam Smith was confronted by at least two people outside Seaford train station, in the city's southeast, on November 25 last year after stepping in to defend his girlfriend.

Liam Casley, 19, pleaded guilty on Wednesday to using unlawful violence in circumstances where his conduct would cause a person to be terrified. Scarlett Taylor, 21, has previously pleaded guilty to the same charge.

They'll face a joint pre-sentence hearing on August 2.

A 17-year-old boy who cannot be named was also charged over the incident, while 20-year-old Jack Ledlin is set to stand trial for Mr Smith's murder.

It's alleged that at around 6.45pm that evening Ledlin and the three others began an unprovoked attack on Mr Smith and his partner.

Ledlin is accused of pulling out a weapon during the altercation and fatally stabbing Mr Smith.

He has pleaded not guilty to murder.

Australian Associated Press