Which of the following actions is considered unnecessary roughness?

Unnecessary roughness refers to actions that are deemed beyond the acceptable level of physicality allowed in the sport, typically involving intent or reckless disregard for the safety of an opponent. Pulling an opponent's hair is a clear violation of the rules, as it constitutes an action that is not only aggressive but also potentially harmful. This type of behavior can lead to penalties due to concerns for the safety and sportsmanship expected in wrestling.

In contrast, reaching for legs and maintaining a defensive posture are standard wrestling techniques that do not involve any excessive aggression or harmful intent. Excessive celebration, while potentially unsportsmanlike, does not qualify as unnecessary roughness since it doesn't pertain to the physical contest between competitors. Thus, pulling the opponent's hair is the most definitive example of unnecessary roughness among the options presented.