9:14 AM PT -- According to the incident report -- obtained by TMZ -- when deputies arrived, Obie was holding a pistol and was quickly ordered to the ground and taken into custody.
The report says Obie had allegedly been drinking all day and got in a physical altercation with his girlfriend. The girlfriend's 18-year-old son then intervened, and Obie went to get his gun. A struggle ensued over control of the weapon, and it went off ... striking the son in the groin. He suffered a fractured pelvis because of the bullet.
7:45 AM PT -- Law enforcement sources tell us a neighbor called cops early Friday morning when they heard loud noises and shouting coming from Obie's place. We're told when cops arrived, they spoke with Obie and a woman he's been living with who said they'd had an argument.
Our sources say the woman's son got in the middle of the argument, a gun went off, and the son was shot. The son then drove himself to the hospital for treatment ... he's in stable condition.
The case is still under investigation.
Rapper Obie Trice is in real trouble, no gimmick, after cops busted him for felony assault with a gun and violating a restraining order.
Trice was booked early Friday morning in Oakland County, Michigan on 2 charges, and is still locked up. The charges include aggravated felony assault of a family member with a gun and contempt of court for violating a protective order.
It's currently unclear who he allegedly assaulted and the circumstances leading to his arrest. His bail's been set at $16,900.
Trice was a big part of Eminem's heyday -- he signed to Shady Records in 2000 -- and contributed to songs on the "8 Mile" soundtrack, the D12 album "Devil's Night" ... and of course, had the famous opening line to Em's "Without Me."
He left Shady and started his own record label, Black Market Entertainment, in 2010.