The puppies are so afraid of White Fang they stay together in packs for safety. While chasing White Fang, what happens to the lead dog when he gets too far in front of the others.

From Text ch 11

White Fang had learned to turn suddenly upon the pursuer that was ahead of the pack and thoroughly to rip him up before the pack could arrive. This occurred with great frequency, for, once in full cry, the dogs were prone to forget themselves in the excitement of the chase, while White Fang never forgot himself. Stealing backward glances as he ran, he was always ready to whirl around and down the overzealous pursuer that outran his fellows.