The climbing team had been working the route on a blue toprope. When the lead climber was feeling confident to lead the climb, he went for the lead attempt, using a blue rope to lead on. Critically the toprope was not pulled before the lead attempt took place, as we planned to use it for futher toprope climbing afterwards.

The leader climber up past a section without any gear which risked a ground fall, he was aware of the groundfall risk and was moving carefully. After reaching the safety of good holds and a solid nut placement, he clipped the rope to the nut's quickdraw and thought he was safe.

I was belaying during this time and when the climber clipped I noticed that the lead rope didn't move at all. I looked up and noticed that the leader had clipped the nut quickdraw to one of the toprope strands and not his lead rope. This meant that he was totally unprotected despite thinking that he was safe. I called up to him and asked him to check his ropes, he clipped his lead rope into the protection and continues his lead climb without any injury.

This near-miss could have had a terrible outcome, especially if the climber had let go of the wall to rest of the rope after his initial (mistaken) clip as he would have thought he was safe.