Two blots up the route diverges into three, It was while assessing which line to take a large chunk of rock I was holding onto came out. Nearby climbers reckoned approximately the size of an under counter fridge. This caught my knee as it fell - ultimately requiring 5 stitches. Belayer was paying full attention and reacted quickly to press against the wall to avoid. People were walking on the path below as well but similarly alert to me climbing above. This could clearly have been an incredibly serious incident that we were luck to walk (limp) away from. Route picked as a warm up and based on guidebook description - 1 Star without falling rock symbol - see lessons learnt.