Four fans are suing US rock band Creed for $2m (£1.3m) after lead singer Scott Stapp was allegedly too intoxicated to sing at a concert near Chicago last year.
The band are one of America's most popular rock groups
The fans claim that Stapp was incapable of singing the lyrics to any of the songs at the gig on 29 December at the Allstate Arena in Rosemont, Illinois.
The band, who are known for their Christian lyrics, apologised to concert-goers for any disappointment caused in a message posted on their website.
They also called the performance "the most unique of Creed shows" and told fans: "It's only rock and roll."
But the four claimants allege Stapp left the stage on several occasions during songs for long periods of time, rolled around on the floor of the stage in apparent pain or distress and appeared to pass out during the peformance.
They are hoping to recoup the $227 (£143) they paid for tickets and parking fees.
The lawsuit seeks over $2m in total from the band, promoters Jeff Hanson Management and ticket-sellers Ticketmaster on behalf of the 15,000 fans who attended the concert.
The Florida-based band have had huge success in the US since they formed in the mid-90s.
Their debut album My Own Prison has sold more than six million copies.
Their second and third albums, Human Clay and Weathered, both debuted at number one in the US Billboard chart.
The band won rock artist of the year at the Billboard Music Awards in 1998, 1999 and 2000.
But they have sought to distance themselves from their Christian band tag.
On the band's website, Stapp says many people label them as a religious band because of their spiritual lyrics but he denies they are a Christian band.
"A Christian band has an agenda to lead others to believe in their specific religious beliefs. We have no agenda", says the lead singer.
Creed cancelled part of their US tour earlier last year after Stapp was involved in a car crash.