If you are using the roll take up and you don't tape the media onto it straight, it will skew and creat a tent or ripple effect that the head strikes against and that skid mark.
If you pause the printing when the media starts to touch the floor place three pieces of tape along the edge of the media, crawl under the printer from the back side, push the tension bar foward and pull the media evenly towards you while putting pressure on the tension bar and adhear the media to a take up roll. Press pause to resume printing.