The correct answer is: no article.
The word "volleyball" is a common noun, which means it does not refer to a specific volleyball. Therefore, we do not need to use an article before it.
If we were to use an article, it would imply that we are referring to a specific volleyball. For example, we could say "Let's play the volleyball that is in the gym." In this case, we are referring to a specific volleyball that is located in a specific place.
However, in the original sentence, we are not referring to a specific volleyball. We are simply saying that we want to play volleyball. Therefore, we do not need to use an article.
