Easthill Park in Portslade was sealed off with forensic tape this morning after a teenage boy was attacked with a baseball bat last night.
The 15-year-old victim is in hospital with a serious head injury as a result of the attack, which happened at 8pm yesterday.
Two arrests have been made and police are appealing for any witnesses to come forward.
A spokesman for Sussex Police said: “The victim was sitting on a bench on the northwest side of the park with another male when he was approached by two people, one of whom assaulted him with a blunt weapon, believed to be a baseball bat.
“The victim received a serious head injury and is currently in a stable condition in hospital. The intervention of a member of the public prevented further assault on the victim and caused the suspects to make off from the scene towards the south side of Easthill Park.
“The suspects are described as a firstly a white male, aged 15 to 16 years of age, wearing a dark top or coat. The second male is described as a white male aged around 15 to 16 years of age, wearing a grey hooded top with the hood up and grey tracksuit trousers.
“Police have arrested two males who are being questioned regarding their involvement in this assault.
Sussex Police would like to hear from anyone who witnessed the incident, saw people running away from the Easthill Park area at the time.
“If you have any information relating to this assault please contact Sussex Police on 101 and quote reference number 1393 9th October 2015”