Police in Wiltshire say between 30 and 50 youths gathered in a field in north Swindon to commit large-scale disorder and serious assault.
Officers have told ITV News Westcountry that they believe it was arranged through social media, such as social networking sites.
One teenager was treated in hospital for a knife wound across the lower stomach during the incident in a field close to Haydon End on the evening of Wednesday 6 March.
Wiltshire Police say youths were seen congregating in and around several streets including Prospero Way, Havisham Drive, Hardy Close and Mazurek Way.
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Wet and windy throughout the day with little change.
Wet and windy with little change.