Instructions
Start teaching your dog not to chase with the dog on leash. Roll a ball out in front of the dog and give the verbal command "off."
Give a firm tug on the leash when he starts to go after the ball and give the "off" command again. Do not allow him to get to the ball or he learns to associate the "off" command with the chase instead of with not chasing.
Repeat this training several times over the course of several days until the dog appropriately responds to the "off" command. Give her a treat, and a lot of praise, each time that she gets it right.
Involve a friend for the next step of the training. Have your friend run past the dog. When the dog tries to chase your friend, give the "off" command and tug the leash firmly.
Release the leash, but leave it attached to the dog and dragging behind him. Have your friend run past the dog again. If he begins chasing your friend, give the "off" command. If he does not stop for the verbal command, pick up the end of the leash and stop him.
How to Stop a dog From Chasing People
Chasing is instinctual for dogs. Dogs are carnivorous and wild dogs are predators. In addition to being instinctual, most dogs find chasing a lot of fun. However, most people do not find it fun to be chased by a dog, especially a dog they do not know. If your dog chases a child, the child may panic and run out into traffic or do something else that causes injury.