The rocker panels on the Subaru Legacy Outback are the plastic trim panels under the doors. They mainly serve as a way to hide the frame for looks. Their low position on the car means they can get damaged from being kicked when people enter the car, or from rocks kicked up by the front tires. You can remove the rocker panels and replace them with aftermarket parts, or replace damaged panels with parts from a junkyard or dealer.
Look or feel under the car for a pair of screws at each end of the rocker panel. Unscrew them with your screwdriver and set them aside.
Run your hand underneath the edge of the panel, feeling for five small plastic clips spaced evenly along the length. Pull the clips out as you find them. Save the clips.
Carefully pull the rocker panel away from the body. It should come off easily. Repeat for the other side.
