The Walkin' on the Sun hitmaker was performing at the Taste of Fort Collins festival when he halted his band's set and reportedly threatened audience members who were trying to pelt him with bread.
In video footage of Harwell's tirade posted online, he says, "You throw one more piece of s**t on f**king stage, I'm gonna come find your a**, I'm gonna beat your a**, whoever the f**k you are out there.
"You wanna be a bada**? Come up here. Come on. Come be a bada** up here. Come on! Come onstage! Come onstage, bada**! Come on! Come onstage! You bring your a** onstage, whoever's throwing s**t at me!"
According to the Coloradoan, Harwell was subdued by a bodyguard and subsequently walked off stage before the band's encore.
It is unclear why the unidentified fan or fans chose to hurl bread at the singer during his set.