Lead climber is being lowered from 10 clips up. At about the 8th clip an overhand knot in the middle of the rope reaches the tube type belay device. The belayer starts climbing up the wall. The belayer is near clip 3 when I become aware of the situation and ask them to climb back again so that I can then undo the knot for them. There were many people around who would've been willing to help if called.