NSW man critical after scooter bashing

A 55-year-old man remains in a critical condition after he was bashed over the head with a scooter after intervening in an argument between a young man and woman in Sydney's inner-west.

A 21-year-old man who was arguing with a 21-year-old woman allegedly hit the man with the scooter after the older man spoke to him while they were walking along a Marrickville footpath at lunchtime on Saturday.

The victim fell to the ground and the 21-year-old walked on, throwing the scooter into the front yard of a nearby house, police said.

The injured man was taken to Royal Prince Alfred Hospital where he remains in a critical but stable condition.

The 21-year-old man was arrested on Saturday and released, but rearrested on Sunday and charged with recklessly inflicting grievous bodily harm.

He was refused bail and is set to face Newtown Local Court on Monday.