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That'll leave a mark!

10 Things I Hate About You actor Andrew Keegan was tasered by police after officers visited the scene of a party he was throwing in Marina Del Ray, Calif., Saturday.

Keegan, 32, was pulled aside after reportedly receiving a noise complaint, and reports the actor became "very aggressive" when cops asked him to turn his music down.

Though TMZ reports Keegan was not arrested, the police altercation left the actor -- and his party guests -- reeling.

"He was tasered right in front of me," one eyewitness tells Us Weekly. "Oh my God, it was so awful."

Another partygoer tells Us LAPD helicopters were circling the Venice Beach area as 15 police officers descended on the residence.

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"He was throwing a block party [and I] saw it happen," says the witness of Keegan, who also appeared on The WB's 7th Heaven. "You could tell he was in pain."