A teenager was stabbed in the neck after asking a group of youths to stop throwing snowballs in Sheffield.
Police said the 19-year-old challenged the group for throwing snowballs "aggressively" at people in the street and at passing cars.
A police spokesman said the victim was kicked, punched and stabbed in the neck, possibly with a broken bottle.
Police have only just released details of the attack, which happened in the Upperthorpe area on 2 December.
The group was made up of up to 15 youths and the attack took place between 2000 GMT and 2015 GMT near to the Continental Food Store at the junction of Upperthorpe Road and Addy Street.
The injured man required surgery and was later allowed home.
The group also assaulted the victim's 19-year-old friend, who suffered cuts and bruising to his face.
The attackers were aged between 15 and 20.
Witnesses or anyone with information are being asked to contact police.