Four of us (the pair directly involved in the incident and us) are friends; we had approached the crag together and planned to climb two of the easier routes in the north wall area. The incident occurred on the route Bacchanalian. This is on the upper tier of the North Wall area at Wintour’s Leap. The pair were climbing comfortably within their grade and were familiar with the area and rock type. The partner ("P") had previously led every other HS route at the crag, so was particularly familiar with it, and had previously seconded Bacchanalian. The weather was good. The casualty ("C") was belaying from a tree at the top of the first pitch. Everything had gone well up to this point (including their previous route on the lower tier). 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 down climbed to C as quickly as was 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). My partner and I had just set up an abseil at the top of Left Hand Route, which is about 20 metres away. 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. 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 ambulance call centre and C&P (mediated by my partner, who had line-of-sight to both of us). My partner checked the crag for other climbers near by who could help. Initially there was nobody else climbing on this wall. C was initially knocked unconscious and then came round but was concussed and very confused. C became gradually less confused during the rescue, but had significant increase in the facial swelling (head and face) during the time waiting for the emergency services. The block was pressing on C's ribs, so P was unable to assess this injury as they not want to move the block in case this led to it falling down the cliff. Emergency services were called at 15.17. They arrived on scene initially at a different part of the crag (much nearer the easy way down viewpoint). They did locate us relatively quickly (my partner used a whistle and bright clothing to attract attention). I had given "what three words" location. After 45-50 minutes, we made direct contact with emergency personnel who were in the garden above. A further team also approached below after a further approx 20-30 mins. The lower team reported they were assessing the option of lowering C to the ground. Multiple agencies attended: fire, ambulance and police, from both South Wales and South West England. A team on the ground and one above referred to themselves as HART (Hazardous Area Rescue Team). The first emergency professional to be winched from above was “Fireman Sam”. They descended with caution, to the side of C&P, due to the ongoing concern about loose rock. However, the second person to lower to the incident with the stretcher (who we believe to have been from the HART team) initially did not listen to Sam who was warning that they was approaching over the loose rock. P had to reinforce this, shouting up that (smaller) rocks were being dislodged and landing on them. This same person dropped a plastic bottle down the cliff while descending and made no attempt to shout out (this was left to my partner to notice and shout) despite there being people on and below 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. This concern of a significant head injury was escalated to Fireman Sam. It seemed that my partner (who is a medical practitioner) and another climber who had arrived at the ledge by this time (and happened to be a paramedic) had to be very assertive to insist that C be rescued up to the top of the crag (less than 20m) and straight to a waiting ambulance using the equipment by now in place, rather than descend over 50m via multiple abseils to the bottom of the crag followed by a significant carry as proposed by HART. C was admitted to hospital and underwent various tests and therapies but was luckily discharged with a minor head injury, soft tissue injuries and a possible facial fracture.