A 19-year-old boy was stabbed in the head after trying to break up a fight between two teenage gangs.
He was also knifed in the torso after getting in between the group of about 15 to 20 youths in Bow on Friday.
The victim was walking along Alfred Street at about 3.45pm when he came across the violent scenes.
Two groups of youths, all thought to be aged 15 to 16, had set upon each other.
The victim was taken to hospital but discharged over the weekend.
He is not believed to have suffered any serious injuries.
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