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.