The first time you're at an Ultimate game you might notice a lot of singing going on at the end of a game. At the end of each game each team creates a customized cheer to salute their opponents. Usually it consists of taking a song that everybody knows and making up lyrics to commemorate the fun you had playing with your opponents. Recounting the game's highlights is nice, a little friendly slagging doesn't hurt, and naughty lyrics are welcomed. If you feel you can't sing or aren't very good at coming up with words, don't worry.
Enthusiasm counts more than talent when it comes to the cheer.
It's just another extension of Spirit.