A 53-year-old man was smashed over the head with a glass bottle and stamped on for criticising a woman's parking.
The victim was assaulted in Preston Park in Brighton after he confronted a man and a woman telling them they could not park their car on the grass shortly after 6.30pm on Thursday May 15.
The 53-year-old from Brighton talked to the man but then turned and went to walk away when his attacker clouted him over the head with a glass bottle and stamped on his head when he fell to the ground.
The attacker then got into the passenger seat of the silver Ford Fiesta they had argued about and the woman drove it away.
He was described as white, about 6ft and muscular and was wearing grey shorts and a luminous green or yellow t-shirt.
The victim suffered serious cuts to head and bruising to the cheek.
A 23-year-old man was later arrested on suspicion of wounding with intent. He was questioned before being released on bail until July 9.
Detective Constable Shirley White said: "I need to speak to anyone who was in or around Preston Park on Thursday evening and saw or heard any of what happened.
"The victim has suffered very nasty injuries which could have been far more serious if he had not been helped by other people in the park after the attack.
"If you know anything at all please contact us."
Anyone with information should call 101 quoting serial 1228 of 15/5, email firstname.lastname@example.org or call the independent charity Crimestoppers anonymously on 0800 555111.