Smash Mouth's frontman Steve Harwell jeered "f**k that COVID shit!" to a crowd of thousands this week, ignoring social distancing rules while the US suffers the devastating coronavirus pandemic.
The Washington Post referred to the audience at South Dakota's 80th Sturgis Motorcycle Rally as "the unmasked masses", with face coverings encouraged but not required at the annual event.
Footage of the gig reveals many maskless audience members tightly packed together and according to USA Today, festival-goers who travelled from virus hot spots did not have to quarantine.
Harwell can be seen telling the crowd: "We're all here together tonight! F**k that COVID sh*t!" in videos circulating on social media.
The band has stood by its decision to play the show, with manager Robert Hayes telling Billboard they were "very happy with the outcome".
"Everything backstage was sanitised, etc. The band has their own COVID-19 addendum to their rider as well and the promoter and venue adhered to all of our requests," the email statement read.
"We spent endless hours advancing this event to make sure that it was pulled off as safely as possible."
The 10-day-long motorcycle gathering is expected to draw 250,000 guests this year, with musical performances from acts such as Buckcherry, Drowning Pool and Bone Thugs-n-Harmony yet to come.
The COVID-19 pandemic has so far killed more than 163,000 Americans, with over 5 million confirmed cases reported nationwide.