Climbing at Long Quarry Point on route called Shelf Life. Got to belay, and heard and then saw a head sized rock miss me by about 2 metres. Then missed my belayer at the foot of the climb by about the same distance. Coastguard were doing some training nearby and witnessed some kids at the top of our route. So likely them that either dislodged or threw the rock down, although unlikely that a rock was dislodged given the nature of terrain and scarcity of loose rocks in that area. Whether they knew we were there or not is not known.