Can you idientify which chick did it? If so you could try removing it and then putting it back with the others after a day or so, when it should be at the bottom of the pecking order. Very unusual for pecking order shenanigans in such young chicks, though. Do they have 24-hour access to chick crumbs? If not they'll peck at anything when they get hungry and once blood is drawn the red colour it very attractive to them. If not already under an infra red lamp you could try using one as it makes everything look red.