Here is Cavalera's side of the story. 
He claims he was forced off the stage by an Atlanta City Police officer after getting involved in an altercation between security personnel and fans. Cavalera claims that the security force was out of control, "running roughshod over fans" during the Soulfly performance.

He proceeded to pull one guard off of a fan, which led to another officer grabbing him and pulling him from the stage and placing the frontman in a room back stage. He also claims that the officer "verbally berated" him and forced him back on stage to make an apology to the security personnel with the threat of arrest. Cavalera did as ordered and told the fans that the band was not into violence. 

The story doesn't stop there, after the show the same officer pulled his gun on Cavalera as he was attempting to drive away from the venue. The officer pulled Cavalera from his car, placed him in handcuffs and escorted him past the singers children and Soulfly fans back into the venue to make another apology to the security staff.  

The City of Atlanta police department has been silent on the matter, but Cavalera's legal team is asking that they launch a investigation into the incident and issue a public apology to the frontman and the bands fans.