A 16-year-old Muslim boy was wounded at a religious festival by a Sikh wielding a ceremonial sword.
The festival has passed off without incident in previous years
West Midlands Police are treating Sunday's incident at the Vaisakhi Mela in Walsall as racially aggravated.
Faisal Mehmood says he was hit with a sword before it was unsheathed and his arm was slashed.
Two Sikh pupils have since been attacked at a college in the town in what the head teacher believes was an act of reprisal.
One of the students at Joseph Leckie Community Technology College was struck with a metal bar by a gang of youths on Monday.
Police say they think the earlier incident at the festival, which was held at the Walsall Arboretum, was racially aggravated.
They are also investigating claims that a small group of Muslim youths caused trouble at the event by showing disrespect to the Sikh religion.
The Vaisakhi Mela is a celebration of the Sikh religion, and Sunday's gathering was billed as a community event that was open to all.
Faisal Mehmood told BBC Midlands Today he was set upon by a group of attackers.
"Some men grabbed my hooded top and started hitting me on the back with the samurai.
"It was in its case but then someone took the case off and slashed my arm.
"By that time the police had come around and the Sikhs ran off."
Swords and spears
Faisal's father Khalid Mehmood said: "The police were there and I confronted them and I said: 'Why did you let it happen?
"Why do you let people carry swords and spears in a family outing like this?'"
Harvinder Singh, a police officer who was off duty at the event as one of the organisers, said: "The Sikh Forum condemns this sort of behaviour and I think as a community we should rally together and find out exactly what happened."
Representatives of the Sikh and Muslim communities are due to meet on Thursday to discuss Sunday's events.