A man who was attacked by a group in a park after he went to protect his son is in hospital in a critical condition, family friends have said.
Alan Willson ran from his home in Worthing, West Sussex, after his son called him to say he was being attacked.
The 46-year-old was taken to the Royal Sussex County Hospital in Brighton, where he remains in a coma.
Five boys have been arrested and released on bail under "strict curfew".
Rhiann Wiseman, who has set up an online appeal to help Mr Willson's family, wrote: "Alan's son rung him to say he was in trouble in Longcroft Park, he went round to see what was happening to his young son and was brutally attacked.
"He is now in a coma after being beaten. His son saw the whole thing."
Sussex Police said they were called to Whitebeam Road at about 19:30 BST on Sunday after a man had been found injured in nearby Longcroft Park.
A police spokesman said: "Four boys were arrested on suspicion of attempted murder and grievous bodily harm with intent.
"They were released on bail with conditions while police enquiries continue. These conditions include strict curfews, staying at a given address away from the local area and not associating with each other.
"Police also arrested a fifth boy on suspicion of attempted murder on Monday. He has also been released on bail with strict conditions."
Police are keen to hear from anyone who witnessed the attack.