Man in custody over Anzac Day assault

A man is being questioned over an Anzac Day attack on a Sydney train that left a Navy officer bloodied.

The 24-year-old serviceman was in full uniform returning from the Anzac Day Memorial Service on Monday afternoon when he approached a group of young men drinking and harassing commuters.

His partner, Emma Novotny, took to social media to describe the group as "openly drinking, swearing, and disrespecting Anzac day in front of veterans and families with young children".

"My partner being a current serving member of the Defence Force stepped in and stood up to the people that were being disrespectful," she said.

The serviceman was punched in the face and suffered a bloody nose as he got off the train at Glenfield a short time later.

The attacker fled the scene.

Police said a 27-year-old man, accompanied by a lawyer, handed himself in at Macquarie Fields police station on Tuesday afternoon and is assisting with inquiries.