The most dangerous sport? Cheerleading.

From ABC News:

[...] Cheerleading has long been an iconic American pastime, and it is now more popular than ever. By one estimate, 3 million young people cheer, more than 400,000 at the high school level. And cheerleaders are no longer only on the sidelines -- many cheer competitively.

The degree of difficulty of cheer stunts has exploded. So too has the number of accidents.

Cheerleading emergency room visits have increased almost sixfold over the past three decades. There were nearly 30,000 in 2008, according to the Consumer Product Safety Commission.

The numbers are all the more disturbing because some states don't even recognize cheerleading as a sport. That means there are no uniform safety measures and training methods.