Young Thug performed last night at the Southside Event Center in Pittsburgh.

When he was leaving the venue, security saw somebody in Thugger's entourage with a gun.

That led to a tense scene in which a large SWAT Team descended upon Thug's van.

Luckily, calmer heads prevailed. The cops did find four firearms in the vehicle, but they all came with proper papers and nobody was arrested.

Check out video of the chaos: