Mutton busting is an event held at rodeos similar to bull riding or bronc riding, in which children ride or race sheep.

In the event, a sheep is held still, either in a small chute or by an adult handler while a child is placed on top in a riding position. Once the child is seated atop the sheep, the sheep is released and usually starts to run in an attempt to get the child off.

The vast majority of children participating in the event fall off in less than 8 seconds. Age, height and weight restrictions on participants generally prevent injuries to the sheep, and implements such as spurs are banned from use.

Via Wikipedia.