Police were attacked and injured following a disturbance involving more than 30 youths in the Cynon Valley.
Three officers suffered minor injuries during the incident that centred around Darran Road, Mountain Ash, at about 20:00 BST Saturday.
Three youths, aged 14, 15 and 17, have been arrested in connection with the incident.
One resident said: "I've never witnessed anything like it before, they were like a pack of animals."
Residents also reported threats being made and damage to property.
Police are investigating to identify all others who were involved in the "delinquent behaviour" and said it "won't be tolerated".
They have also called on parents to take responsibility.
Police Inspector Rob Blunt, said: "We are treating this incident very seriously indeed.
"All those involved can expect a knock on their door and a visit to the police station shortly.
"Parents of youths in the town and surrounding areas can take some responsibility as well.
"Anybody who cannot be sure of the movements and activities of their children during the evenings and on weekends should be asking questions."
Local councillor and Rhondda Cynon Taf council leader Andrew Morgan said he was "disgusted" by the incident.
Disgusted to hear that several @SWPCynon officers have been assaulted in a disturbance in Mountain Ash town centre this evening involving a large number of youths. Understand that several arrests have been made.— Andrew Morgan (@AndrewMorganRCT) October 27, 2018