Is bullying considered a form of sadism?

Certainly can be: Bullying can indeed become a sadistic behavior: taking personal enjoyment and excitement from another person’s suffering. In a “normal” competitive confrontation, when a person has achieved their victory they stop. But a bully (with sadistic urges) will keep going -- listening to their victim’s pain and playing on it to increase the misery. The power is one-sided, and dominating.