OK, so if I come to your house, ask your permission to do something, you OK it, and someone gets hurt, who pays? Your homeowners insurance. Thus, your liability.
I studied the business end of the recording industry in college. Started as my major in fact. Nearly every performance contract at that level (clubs) plainly states what is and what is not permitted. It also states that the final call lies with the club owner as they carry the liability insurance. They have a business license to protect. If a performer is hired to provide entertainment, they do so under the club's terms. Therefore, anything that a club owner allows in his club is on his head if it goes bad. At least, that's what they taught us.