Cheerleading is mainly used to egg on sports men and women. They hardly play a role in the game apart from keeping the men awake by looking sexy and making a lot of noise, preferably more noise than the rivals cheerleading team.
However you do get tired from all of this movement and that counts as exercise and all sports require exercise and activity (I am excluding snooker and darts. I do not class them as sports, I class them as games instead.)
You can also link cheerleading with dancing since dancing is a sport (they do it in the olympics so don't start an argument whether dancing is a sport or not). A dance requires a pre set up routine and so will a cheerleading session. I think the only difference is the fact that dancing is more well know and likely to be graded, where as cheerleading is just accepted into a basket ball match with no review!

Cheerleading is a Sport!