Dogs kick to spread their scent and mark their territory after pooping.
Scent Marking
The kicking motion mimics burying poop as dogs would do in the wild.
Burying Poop
Kicking may be an instinct to clean their paws and cover their business.
Hygiene
Some dogs scratch and kick out of joy and relief after pooping.
Joy and Relief
Kicking can express anal glands or relieve discomfort from full anal glands.
Anal Glands
Kicking can become a habit. Use positive reinforcement not to reward the behavior.
Training
See the vet if frequent scooting or licking occurs along with kicking.
Medical Causes