The Shasha that Xiaopang calls is Sun Yingsha.
According to the official website of Query Entertainment and media interviews, Xiaopang refers to Fan Zhendong of the table tennis team, while Shasha refers to Sun Yingsha of the table tennis team. During the World Table Tennis Championships trials in Durban, there was an interview with Fan Zhendong. He once said that both Manyu and Shasha had tried to play mixed doubles, so Sun Yingsha should usually be called Shasha.
In fact, it is normal for good friends to call each other by their nicknames. After all, fans also call Sasha that way.