This happened back in the late 70's at a DZ in Charlotte Michigan. A load of us went up in the 182 for a four way. Things may have changed in the years since, but back then it was popular for some jumpers who thought they knew better to load the plane in various stages of dress. Some would walk on with the jumpsuit and rig in their arms. Others with a jumpsuit on and the rig riding their shoulders, and others all geared up ready to exit. Our ride up was uneventful and the exit went as planned. Our hero was wearing a Stewart Sweethog container system with a square main and round reserve. In freefall, we were so focused on completing formations that not even the jumper himself noticed that he had forgot to put the leg straps on ... that is until it was time to open. The jumper whipped out his pilot chute and as opening occurred, slid down the harness until the junction at the main harness caught in his armpits. This was opening shock #1. Due to uneven loading on the risers, the jumper had a malfunction. From my perspective some 30 yards behind and above, I could tell a cutaway was ahead and thought something didn't look right, but things happened so fast I didn't realize at the time how wrong things were for the guy (in?) the harness. Somehow he managed to cut away the main and deploy his reserve without falling out. Opening shock #2. He rode the rest of the way down grabbing harness with crossed arms, unable to control his direction. The landing was brutal but he was so rattled he didn't even care. He was incoherent most of the rest of the day and almost gave up jumping. Even thinking back on that day, as I write this, it makes my pulse race and palms sweat. We crucified ourselves for not doing gear checks, but it happened. and maybe others can take home a lesson.