Soulja Boy has been arrested for violating his probation by possessing ammo.

The cops spotted the ammo last month when they responded to a call that the Big Draco had held a woman hostage in his garage. (He said he didn't, and wasn't charged.)

But they waited to arrest him until today when they knew he was scheduled to meet his PO.

SB has been on probation since 2010 on weapons charges and has been told he can not possess anything related to weapons.

The rapper's currently in jail in Van Nuys, California and will appear in court later today. He's scheduled to perform at the Clippers game tonight, but that may be in jeopardy