Air ambulance and ambulance called after large rock fall. Unknown exactly what happened - climber was apparently knocked unconscious but seemingly not otherwise seriously hurt as was walking. Happened by the Bishops Move/PBA abseil tree halfway up the slab where a lot of rock has come down just below the tree. Large chunk (~2x2'?) or more has come down and taken a massive section (many multiples of above) out below it.
Hypothesis: looks like either the initial rock came out moving up over the overlap or when stood up on it. Rock fell taking out lower section and climber hit head falling. Lucky no one was killed as the largest section must weight at least a quarter of a tonne at a guess.