Four of us (the pair directly involved in the incident and us) are friends; we had approached the North Wall at Wintour’s Leap together and planned to climb two of the easier routes. We are all reasonably familiar with the area; in particular, the person who was leading at the time of the incident had led every route at grade HS at Wintour’s Leap except Bacchanalian (which they had seconded previously).

It was a warm, pleasant day with no forecast of rain. We all geared up (including helmets) and took photos of the relevant guidebook pages to avoid carrying books up the crag. We were all expecting to enjoy a morning climb and to descend (by abseil) for a late lunch.

We set off up Left Hand Route while the other pair started on Right Hand Route. They were climbing comfortably within their grade. When they reached the Great Ledge, the other pair decided to climb Bacchanalian, with the partner (“P”) leading both pitches. The first pitch went fine.

At the time of the incident, the casualty ("C") was belaying from a tree at the top of the first pitch. P had started up the second pitch and had gone about 5 metres. P was testing all the rocks for looseness by tapping them gently. P was trying to work out the next move when a large boulder dislodged; they did not pull on it so it must have been very loose. But it was also a substantial size, so would not have sounded hollow, as smaller pieces commonly do. P shouted a warning and C moved to try to avoid the boulder. The boulder hit the tree, which absorbed some of the force, then C's helmet (which is severely dented) and landed on C's left side, partly trapping them. P saw C was unconscious and downclimbed as quickly as possible while staying safe, and made them both safe with slings to the trees. (Importantly at this point due to the shout of “Below”, a 3rd pair of climbers on the ground were able to move out of the way and admit they otherwise may have been hit by the other debris that fell with the large block).

My partner and I had just set up an abseil at the top of Left Hand Route, which is about 20 metres away. We heard the call and the sound of debris crashing down.
“Are you OK?”
“Call an ambulance”
I stayed at the top and called the emergency services, requesting ambulance and mountain rescue, and stayed on the line to them relaying messages between the call centre and C&P (mediated by my partner, who had line-of-sight to both of us). I gave "what three words" location at the request of the emergency services.

Meanwhile, my partner abseiled, initially to be level with the accident, but could not get line of sight, so moved down to the ledge where Bacchanalian starts (The Great Ledge). My partner could not safely reach C and P, but could easily hear P. They checked the crag for other climbers nearby who could help. Initially there was nobody else climbing on this wall.

As noted, C was initially knocked unconscious and then came round but was concussed and very confused. C became gradually less confused during the rescue, but the swelling on their head and face were growing. The block was pressing on C's ribs, so P was unable to assess this injury as they did not want to move the block in case it then fell down the cliff.

P was with C the whole time and kept them talking, checking pulse, respiratory rate and alertness. There was concern that one of C's pupils was not responding to light and there was significant swelling. These concerns were relayed to the emergency team when they arrived nearby.

Emergency services arrived on scene initially at a different part of the crag (much nearer the easy way down viewpoint). They located us relatively quickly (my partner used a whistle and bright clothing to attract attention). After 45-50 minutes, we made direct voice contact with emergency personnel in the garden above the crag. A further team also approached below about 20-30 mins later. Since C&P were less than 20 metres from the top of the crag (and at least 60 metres from the bottom) it made much more sense to winch them up to a waiting ambulance than to lower them to a long and rough walk-out, though both options were discussed. We were relieved to see C disappear up over the edge on a stretcher, followed by P, who was also winched up to safety.

C was admitted to hospital and underwent various tests and therapies but was luckily discharged with a minor head injury, soft tissue injuries and facial fractures.