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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Most places will stay dry but there is the chance of the odd heavy shower, especially south coast during the afternoon.
Rather cloudy, especially to begin with but brightening up.
It will be an overcast evening with clouds persisting into the night.