When a festival is co-headlined usually one band has the right to close the show. For whatever reason Slipknot is closing the Rockstar Energy Mayhem Festival thing. I am guessing it is because they have 100 members in the band, while co-headerliner Disturbed only has five. Stage logistics with tear down and setup would be a pain in the ass setting up 8 instruments then tearing them down quickly for Disturbed to close the show.
 
Altitude TV recently conducted an interview with Five Finger Death Punch's drummer, Jeremy Spencer. He claimed that Disturbed was stealing the show.
 
"We toured with Disturbed [before], but the production was a little more scaled down then compared to this, so seeing them in that set-up, to me, they're stealing the festival, man. I love it." Five Finger Death Punch vocalist Ivan Moody concurred: "I hate to say it, but they're [Disturbed] handing even Slipknot their ass."