The incident occurred when climbing in the lead area of the climbing wall. I was preparing to belay my partner when a climber fell from the top of the overhanging section of the wall, hitting the ground and very narrowly missing me and others nearby. The climber was tied on correctly and being belayed using a non-autolocking device. It was very busy and noisy in the wall at the time, and the belayer was standing right next to the bottom of the route, underneath the overhang. As their partner was at the top, due to the shape of the wall they did not have visual contact.
What appears to have happened is that the climber was at the top, having clipped the lower off, and let go, leaning back onto the rope ready to be lowered down. The belayer did not realise this, and thought that the climber was pulling rope through to clip so let it run through their hands. Once they realised their mistake the climber was falling and the belayer was unable to catch the rope, so it ran all the way through the belay device without slowing the fall at all, leaving the climber to hit the ground.
The climber sustained lower leg injuries.