A 12-year-old boy was head-butted, repeatedly punched and knocked unconscious.
Sussex Police are appealing for witnesses to the assault on the boy in Marine Parade, Hastings.
The victim was playing football with friends at 7.10pm when he was attacked.
There is believed to be one suspect, who is described as a white 15-year-old boy, 5ft 7in of average build with freckles and long wavy brown hair.
He was wearing a blue hooded top and was carrying a black bag.
Anyone with information is asked to call 101, email firstname.lastname@example.org quoting serial 1257 of 5/4 or call Crimestoppers anonymously on 0800 555 111.