The case against an off-duty security guard charged with the drowning death of a man whom he allegedly pushed into Sydney's Darling Harbour is "fundamentally flawed", a court has been told.

Ehab Taleb, 23, has pleaded not guilty to the manslaughter of Jason Daep, 19, following a nightclub brawl at Pontoon Bar at Cockle Bay in the late hours of February 12, 2012.

Mr Daep had been partying with friends at the bar when several brawls between 20 men erupted on the adjacent wharf.

Police allege Taleb assaulted Mr Daep before pushing him off the wharf.

Mr Daep's body was recovered from the water hours later.

At Taleb's committal hearing on Friday at Downing Centre Local Court, the court was told Mr Daep was pushed "forcefully into the water" by a "tall man in a black shirt".

Witness Nathan Truman said he saw the man, who he later identified four months after the incident, pushing an "Asian man wearing a white shirt" into the water.

"The tall man was pushing everyone out of the way ... and then he turned to the Asian gentleman, and his hand came forcefully ... on his chest," Mr Truman told the court.

"The Asian man (then) went further out to the water."

But Taleb's lawyer Grant Brady told the court there were several issues in the identification provided by witnesses.

He said Mr Truman and another witness, a close friend of the deceased, were "tainted" in their identifications because they were provided after they saw Taleb being handcuffed and arrested on the night.

"The submissions through identification is, in my view, fundamentally flawed," Mr Brady told the court.

He said Mr Daep's friend, who tried to pull him from the water, had identified the man who pushed Mr Daep as a "blonde man".

Taleb is of Middle Eastern/Mediterranean appearance.

Mr Brady said there was confusion on the night because there were several fights happening at once, which may have affected the validity of eye-witness accounts.

The hearing before Magistrate Jennifer Giles continues.