As the rookie on the team, he became the waterboy who fetched towels and drinks.

waterboy 是由 water（水）和 boy（男孩）组成的复合名词，字面意思是"送水的男孩"。在体育团队中特指负责为队员提供饮用水和毛巾等后勤工作的新人或助理人员。