Discuss the relationship between sport and multiculturalism (as a speech topic). How does sport specifically bring together people from all cultures? Are there many examples of this truly happening?

A good example of how sport can bring together people of different cultures is the 1995 Rugby World Cup.
This world cup happened less than five years after Apartheid had come to an end, and the country of South Africa was still divided despite having recently become a democracy. The sport of rugby was seen by the public as belonging to white people, and not many black people watched the game.
In addition to the internal conflict catalyzed by Apartheid (that endured in its absence), South Africa had also been isolated from the outside world during the oppressive regime. The South African rugby team, the Springboks, had never played in a Rugby World Cup before 1995 due to anti-apartheid boycotts.
The president of South Africa at the time, Nelson Mandela, wanted to unite black people and white people in South Africa behind a common cause: supporting the national Rugby team. Both Nelson Mandela and Desmond Tutu adopted the term "Rainbow Nation" to describe South Africa, and Mandela often repeated the slogan "one team, one country." As Mandela said in an interview (linked below), "Sports are a language spoken by everybody."
This game is significant not only because it brought South Africans together but because it showed the progress the country was making on a world stage; everybody who watched the game could see that South Africa was becoming a more united country.
For further information about how Mandela and the Springboks captain, Pienaar, worked together to bring South Africans behind the national team, you can read the book Playing the Enemy by John Carlin (there's a review of the book linked below).
http://news.bbc.co.uk/sport2/hi/rugby_union/international/3772591.stm

https://www.nytimes.com/2008/08/17/books/review/Keller-t.html

https://www.youtube.com/watch?v=9Wh4MPGp68A