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KANSAS CITY, Mo. — Nearly 55,000 hard rock and heavy metal fans packed into Penn Valley Park last Saturday for the 20th annual Rockfest. But a video from the event now going viral online appears to show that not everyone was there to have a good time.

The event last Saturday – an 11-hour hard rock extravaganza featuring bands like Shinedown and former Guns N’ Roses guitarist Slash, and sponsored by radio station 98.9 The Rock – was a largely peaceful affair.

But a YouTube video from the event making the rounds on the Internet shows an ugly incident in which a male concertgoer is seen kicking a female concertgoer in the chest before he is taken down and beaten by several bystanders.

The people in the incident are not identified in the video, posted to YouTube on Tuesday by “bstevenskc.” By Wednesday morning, the video had been seen by over 35,000 viewers before it was taken down from YouTube on Wednesday afternoon.

Rockfest is billed as the largest one-day music festival in the nation.