What is the fine-grained topic of the following text: It has just been announced that rugby player and Springbok captain, Siya Kolisi, is now an advocate for the Global Citizen Festival: Mandela 100, a free-ticketed event on Sunday, 2 December 2018 at the FNB Stadium in Johannesburg, South Africa. Only return the topic.
Siya Kolisi as an advocate for the Global Citizen Festival: Mandela 100