Seconding climb to finish off day. Drizzle of rain here and there, group new to particular crag but familiar with area. Combination of RCI assessed and trained climbers. Loose, choosy rock at top of the whole crag let alone the climb. Novelty and grade of climb could have contributed to looser terrain. When pulling out of the last slab on the right, climbers hold broke and pulled rock approximately the size of 2 microwaves onto himself. In turn boulder hit climbers right leg leading to a broken knee and soft tissue damage. Climber got hauled on a 3:1 system and carried to closest access road.