Baltimore City police are investigating a vicious attack in which a security guard was knocked out at the Horseshoe Casino.

(Warning: The video above contains graphic footage.)

The video shows several men attacking a security guard early Sunday morning. One of the men can be seen delivering the knockout blow.

The casino issued a statement saying most customers are responsible and only a small percentage cause issues.

"In the rare instance when this occurs, we follow a zero-tolerance policy," the statement read. "As a result, we have issued lifetime bans against the individuals involved in this unfortunate incident"

There is no word on the security guard's condition or charges that may have been filed in this case.