Richard Valadez, 62, was pronounced dead on Sunday at 11:34 pm after being taken to a hospital from the Hollywood Casino Amphitheatre in Tinley Park, authorities confirmed to The Independent.
Slipknot were performing at the venue as part of their Knotfest Roadshow headline tour.
The cause and manner of death were pending as of Thursday afternoon, according to the Cook County Medical Examiner’s Office.
Witnesses told Patch that Valadez initially seemed fine and that he joined in some mosh pits, a common occurrence at heavy metal gigs.
“Basically everyone was jumping around in the mosh pit having a good time and just being friendly roughhousing dorks, as usual for metal concerts,“ witness Anthony Mackey told the website.
According to Mackey, Valadez fell by the mosh pit onto the grass about an hour into Slipknot’s set and went into seizure, at which point witnesses reportedly called for help.
The Independent has contacted Live Nation, which operates the concert venue, for comment.
In July, Slipknot frontman Corey Taylor was seen in YouTube footage demanding his fans back up after the action in the mosh pit became too intense.
He told the crowd he wouldn’t start the next song until part of the audience had backed up sufficiently.