求这句话中为啥要用in which

求这句话中为啥要用in which
Squash is a game in which two players hit a small rubber ball against the walls of a court using rackets.
in which 里面的 In 是不是和后半句的某个词连起来是个短语呢?这句子为啥要用in which
把in which改成that
Squash is a game that two players hit a small rubber ball against the walls of a court using rackets.