After the 2015 and 2019 Rugby World Cups, the Japan Rugby Top League games attracted many new fans including female fans and niwaka fans (bandwagon fans/fair-weather fans). Understanding the characteristics of game attendees could be crucial to retain new fans and expand the fan base. The purpose of this study was to categorize attendees into four segments according to gender and fan types and to compare their characteristics, motivations for attending games, and knowledge of rugby. Data were collected from seven games at five venues from January 12 to 26, 2020. The four segments—male niwaka fans, female niwaka fans, male regular fans, and female regular fans—were compared by one-way analysis of variance. It was found that male regular fans had supported rugby since 1980, while female regular fans appeared after the 2015 Rugby World Cup. Further, the motivations of female niwaka fans and regular fans were different.