Police have condemned the beating of a mother and her daughter with baseball bats, while the attack was recorded with a mobile phone camera.
The women were walking home on the canal path when attacked
The 48-year-old mother and her two daughters, aged 23 and 17, were set upon while walking home by a canal in Reading, Berks, on Tuesday night.
The 17-year-old ran for help, but the gang of four boys attacked the other two women under the A33 road bridge.
The two were later taken to the Royal Berkshire Hospital with head injuries.
The attack lasted for several minutes before the group ran off towards Lower Brook Street West and Wolseley Street.
The term "happy slapping" has been used to describe attacks captured on a video mobile phone.
Police criticised the use of the expression.
Pc Russell Prentice said: "It's the first incident we've had like this in Reading.
"They give it the title of 'happy slapping', which I think is completely inappropriate.
"This is just outright assault and they cannot justify it just for pleasure."
The youth who filmed the attack on his phone is described as Asian, 16-years-old, and of heavy build.
He was wearing a beige padded jacket, a hooded top, and jogging bottoms with elastic around the ankles.
The other three offenders are described as black, about 13-years-old and thin. They were all wearing dark hooded tops.