The rider must stay aboard the bull for 8 seconds. The clock starts when the bull's shoulder or hip crosses the plane of the bucking chutes and stops when the bull rider's hand comes out of the rope or he touches the ground.
The bull rider must hold on with only one hand and is disqualified if he touches himself or the bull with the other hand during the eight-second ride.
The total score possible for a bull ride is 100 points. One half is based on the performance of the bull and how difficult he is to ride. The other 50 points are determined by the rider's ability to match the moves of the bull.
Bulls are judged based on their speed, power, drop in the front end, kick in the back end, directions changed and body rolls (when a bull is in the air and kicks either his hind feet or all four feet to the side).
Judges are allowed to award a re-ride if they feel the bull did not perform at the level of other bulls in the competition depriving the rider of a fair chance to earn a high score.
For the rider's half of the points, judges look for constant control and good body position throughout the ride. Spurring the bull is not required but extra "style points" are awarded for doing so.
Source: Professional Bull Riders, Inc. Web site, www.pbrnow.com