Can a batter remove his helmet as he is rounding 3rd base after hitting a home run over the fence in a highschool game?

the only time a runner can remove his helmet is in the event that the helmet has impaired the runners vision. in that case the umpires would have the decision of the removal being within regulations or not. if it is not then the runner would automatically be out.

Another answer: In MLB, there is no rule prohibiting player from removing his helmet. However, rules in other leagues (college, high school, youth, etc.) may have such a rule. Consult your organizations rule book.